So MUA2 characters "work". At least Gambit does anyway. It's a start since I can't use XML1 or XML2 animations. That makes new characters (Colossus, Moon Knight, and Gambit) without breaking the herostat. I haven't been able to get the 360 DLC stage to load, so I may have to do "hidden" characters like I did on the Xbox.
As a side note, the framerate in MUA2 PSP is HORRIBLE!!! It looks prettier, but I'm pretty sure that's because Savage Entertainment didn't optimize it for the PSP like VV did with XML2 and MUA1. It looks like they just straight-ported the PS2 assets when you look at the visual quality.