You don't need drivers on a PC because they are already built into the OS.
The GP-49 converts the data it receives from the 49-way into signals that are usable by Windows, using its own built-in drivers.
To the best of my knowledge, the X-box doesn't HAVE these drivers built-in, so would need its own custom ones.
Er, I'd say it a little differently (which gets a different view on possiblities).
49way + whiz49 (or AKI) = works, no special drivers needed in windows
49way + "49way 2 HallEffect" circuit = "works"*, no special drivers needed
49way + (unwritten) drivers in windows = works
49way all by itself = does not work on a PC (like a joystick)
49way all by itself = does not work in xbox/ps2
By the same logic, you either need a "special driver", or you need a special hardware before you hook up the 49way. I think the latter is much more likely to happen; I bet the "49way 2 HallEffect" circuit will work as well as it did on the PC (maybe needs different resistors, though). You
still have to go through a hacked xbox/ps2 controller for it to work on the xbox/ps2 respectively, through.
*When I say "works", I mean the output was curved wrong for mame's 49way games. Picture the curve the opposite of whiz49's "progressive" mode.
Edit: corrected the console named.