Can the VA reduce a veteran's 100% total disability rating without a medical exam?

Yes.  But then that depends on what the court said in what can only be described as an Alice in Wonderland bizarre ruling.  

In Reizenstein v. Shinseki the veteran had been awarded "staged" temporary ratings.  As his medical conditions changed, he was initially awarded a rating of 30% for a month then increased to 50% for two years and then to 100% for about a year and then reduced to 30%.  The VA reduced his 100% award to 30% without any medical examination.

Reizenstein argued that the VA could not reduce his 100% rating without a medical exam. The VA argued that the 100% rating was only a temporary "staged" rating.

Reizenstein argued that 38 C.F.R. § 3.343(a) expressly prohibits the VA from reducing total disability ratings without first obtaining a medical examination of the veteran showing improvement.

The federal court disagreed with Reizenstein.  The court in a strange twist of wording ruled that the VA's use of "staged" ratings is a VA "practice" rather than a VA "rule of law".  According to the court then "[a]ccordingly, we also conclude that Mr. Reizenstein's argument ... is without merit. This follows because once the "rule of law" is properly recognized as a VA practice, it becomes clear that the Veterans Court was not applying its own "rule of law," but rather was adopting the agency's interpretation of the applicability of its own regulation." 

In other words, the court with a straight face ruled as long as the VA says its view of its rules is correct, then that view is correct unless the VA's view is...incorrect.  Since the VA viewed the reduction of Reizenstein's 100% rating without a required medical exam was correct, then that VA reduction is correct unless the VA says it is incorrect.

If you are the child of a deceased veteran are you entitled to compensation benefits that your deceased parent may have been pursuing with the VA?

That depends.  As a general rule, a veteran's claim for disability benefits terminates with the death of the veteran. Richard v. West, 161 F.3d 719, 723 (Fed. Cir. 1998). Consequently, when a veteran-claimant dies during the pendency of proceedings on his claim, including an appeal to the Veterans Court, no other party is automatically entitled to be substituted on the veteran's claim for benefits.  In other words, a veteran, upon death, takes his or her benefits with them.

However there are exceptions.  These exceptions are now explained in the recent case of Phillips v. Shinseki.    That case addressed a daughter's entitlement to her father's veterans disability benefits that remain unpaid when he died.  The Court found that benefits that accrued during the veteran's last two years and were "due and unpaid" at the time of the veteran's death are referred to as "accrued benefits" and can be claimed by a person who qualifies as a beneficiary under 38 U.S.C. § 5121(a). An accrued-benefits claimant may pursue the accrued benefits by filing his or her own claim, which is distinct and separate from the underlying veteran's benefit claim.  The key issue though is that the veteran must have filed a claim that is ongoing with the VA in which benefit are pending or unpaid.  If the veteran fails to file for benefits before death, as a general rule the benefits die also.

Does the VA have to show that its own doctors are qualified to examine veteran's disability claims?

No.  In the case of Rizzo v. Shinseki filed a claim for radiation exposure and injury while the government tested atomic weapons at his station: the Marshall Islands Bikini Atoll in 1947.  Rizzo's doctors testifed that his injuries were due to the radiation exposures. In 2006 the VA sent Rizzo to their own doctor who reported that Rizzo was not injured by the radiation.  The VA denied disability based on their doctor's report.  Rizzo argued on appeal that the VA did not present any evidence that their doctor had specific knowledge or expertise in radiation exposures and his medical report should be thrown out.  

The federal court disagreed with Rizzo.  The court ruled that the VA has no affirmative duty to prove the qualifications or competency of their own doctors.

Can a second SSA Judge find that a claimant is more fit than did a prior SSA Judge's finding for the same claimant?

"
Yes.  In 2002 Kathy Poppa claimed SSA disability benefits.  The SSA denied her claim and she appeared before an SSA judge.  That SSA judge found that although she could only perform sit down or "sedentary" work, she was still not disabled.  Poppa appealed that claim to federal court which overruled the SSA Judge and sent her claim back to the SSA for another hearing.

At the next SSA hearing a new SSA judge heard the claim.  That second SSA judge then found that Poppa could perform "light" duty work; e.g., more demanding work than sedentary, and was not disabled.

Poppa appealed that claim to federal court.  Poppa argued that the second SSA judge could not find that she could perform light duty work since the first SSA judge had already found she could only do less demanding sedentary work.

The federal court disagreed.  In Poppa v Astrue  the 10th Circuit ruled that the decision of the first SSA judge was not a "final decision".  Thus his decision that Poppa could only do sit down work was not binding on the SSA.  The court also ruled that the second SSA Judge was then "free" to make new findings about Poppa's ability to work.

Does a SSA Judge have to obtain medical records if the claimant does not provide them?

No, but then again, yes.

Martha Maes filed a claim for SSA disability benefits.  Her claim was denied and she went before a SSA Judge for a hearing.    The SSA Judge denied her disability.  Maes appealed to federal court.  Maes argued that the SSA Judge should have, but did not, obtain the medical records of Maes' own treating physician: Dr. Kimball.  Maes and her attorney did not mention Dr. Kimball to the SSA Judge or list him as a physician on her paperwork.  However the medical records in evidence did show that Dr. Kimball was carbon-copied on other correspondence form other treating physicians.  Maes argued that the SSA Judge was required to obtain  Dr. Kimball's records before issuing his decision.

The 10th Circuit disagreed and then... agreed in Maes v. Astrue.   The court held that "[a]lthough the ALJ has the duty to develop the record, such a duty does not permit a claimant, through counsel, to rest on the record-indeed, to exhort the ALJ that the case is ready for decision-and later fault the ALJ for not performing a more exhaustive investigation." 

However,  in this case, there was evidence of prescription medications for depression. And since the  the SSA Judge did not discuss or review whether or not Maes suffered from depression, the SSA Judge "must recontact the claimant's medical sources for additional information when the record evidence is inadequate to determine whether the claimant is disabled" before issuing a decision.

Will the fact that a federal employee remains employed rule out a finding that she is disabled?

Yes. Federal employees who can no longer perform the essential duties of their assigned jobs may be entitled medical disability retirement benefits from the Office of Personnel Management.  These are commonly called "OPM disability retirement" benefits and are similar to social security disability benefits.

Maples is employed as a secretary for the Department of Veterans Affairs. She suffers from cytomegalovirus infection and sought disability retirement benefits based on her condition. Maples had recently received an increased VA disability rating showing that she could only walk approximately 150 yards and stand for approximately five minutes.  Maples remained employed at the VA and her performance and attendance had been satisfactory.

OPM denied her claim for disability retirement. Maples appealed to federal court arguing that she presented a preponderance of objective medical evidence, including her record of sick leave, to prove her disability, and that the Board did not adequately consider the evidence.

The federal court disagreed.  In Maples v. OPM the court held that since Maples remained employed with satisfactory performance ratings, there was no evidence that Maples'  cytomegalovirus condition is "incompatible with either useful and efficient service or retention in the position" of secretary. Maples' VA disability rating, which bears on her military service, was found insufficient to establish that she was entitled to disability benefits for her civil service with the ... VA.