Sorry they resigned,it was accepted by their superiors, they were no longer part of the US Army, therefore they were no longer on duty no amount of arguing will change that fact. Another fact none that resigned were ever brought upon deseration charges. Nobody said all that deserted joinned the other side but that is what this discussion is about. You are welcome to be your opinion no matter how wrong you are.
BTW just so you know if one of my comrades was caught fighting for the other side, he wouldn't need a brand or a trial for that matter.