It shouldn't be a problem. I don't know much about the Led-Wiz+GP but I'm guessing they show up as keyboard inputs and the buttons on the U360 show up as game controller buttons. So you just configure MAME with keyboard and joystick input. It's a highly configurable program so you shouldn't have too many problems.
Also, I don't know if you considered swappable panels. This is another solution to compromises and with USB connectivity of many encoders/controllers, it's easier than it used to be. Something to think about. Personally, I did make my panels swappable - however, I made it so one panel (two U360s and a trackball) will play almost all the games (trackball can double as a spinner in a pinch, albeit not as fun). Down the road, I can make specialized panels without much issue. I'm not suggesting you do or not do this - just informing you of another option if you're scrambling for space. ;-)