I brought this up to the mame developers since I had a friend who owned a huge chain of arcades, and man, he owns the rights to 1000's of arcade machines that are dead, or have been converted! He was going to just add a place at the bottom of each mame machine with the original board for everything it played (in case anyone came a lookin)
anyway, it is against the mame license to make money using it. It's kinda too bad because it is the only legal use that the arcade companies could make money on (that would help them support the emulation community).
It's, btw, not illegal to williams, or nintendo. But you would be breaking the mame license. So who would be suing is different. But trust me, if nintendo found out, they would sue. Wouldn't have a case, but they would sue anyway