No precedence on appeal of a UMCJ *verdict* but plenty of precedence on SCOTUS-certiori cases, falling on both sides of the coin.
1863, SCOTUS declines authority to rule on tribunal actions.
1867, SCOTUS rules that tribunal actions were improper.
Both cases were civilian defendants. Again, the verdicts were not appealed, defendant appealed the authority to try civilians in military tribunal.
Still more “intricate” precedent to look at.