Wearing Army uniforms is prohibited in the following situations:
(1) In connection with the furtherance of any political or commercial interests, or when engaged in off-duty civilian employment.
(2) When participating in public speeches, interviews, picket lines, marches, rallies, or public demonstrations, except as authorized by competent authority.
(3) When attending any meeting or event that is a function of, or is sponsored by, an extremist organization.
(4) When wearing the uniform would bring discredit upon the Army.
(5) When specifically prohibited by Army regulations.
I dont believe it matters whether its a military court or civilian as to whether he should wear his uniform. Lawyers will tell you to play to the jury and those of the court by looking professional. What is more professional than our dress uniform? Yeah, it may not be in good taste and possibly bring ucmj charges later. But im pretty sure id rather take ucmj than a bs civilian charge. And because of his most likely great conduct he probably wont see anything but an njp if anything at all unless higher up is politically motivated and wants to make an example.
He's wearing his uniform at a rally, clearly in violation of Army regulation 670-1 Ch. 1-10.j.
And he is not on trial as a soldier, this has nothing to do with his military service. He was charged as a private citizen during an off-duty incident and should not be exploiting his service to support his case.