You could get that many leads off of it. Pot= potentiometer. By far the most common potentiometer used in arcade analog joysticks is 5k. In order to interface the joystick to an xbox controller, you would need to change the values of the potentiometers in the joystick before it would interface properly with the controller. It may work with the 5k, but I don't think you would get full left to right and forward backward motion if you see what I mean. As far as the Xboxmame compatibility with games, I'm sure you would just have to do your research on the subject, I have it on my xbox, but I only played one game, It was a overhead flying game, I think it was like 1942 or somethin like that. However, if you are only looking for classic games, like frogger, DK and such, there are excellent ports of the Atari that would do the trick if nothing else. I'll look into the compatibility and let you know what I come up with, as far as a Linux detro mame, haven't heard of anyone doing it, I never really messed around to much in xbox Linux because I never saw the point as I have a computer.
You could actually get 2 more buttons out of it, don't forget the 2 under the thumbsticks.
!!!Update!!! Seems the mame ports you can get for the xbox are quite stable. Not sure if I can link to another site from here. Need read the rules.