Hi,
the link above is obsolete (old version - crappy implementation).
RGBcommander's site contains relevant information in the MAME section with one exception.
->
http://forum.arcadecontrols.com/index.php/topic,151464.0.html -> read my post - not yet in place - eta unknown
regarding the outputs - I only support the flashing led outputs like blinking insert coin.
I don't know if any of the mame derivatives popular on the pi have a functional output system in place.
'real' mame has/had (depends on the version) it but the pi is too slow to run it.
so, the answer is it is supported to a certain degree if you follow a whole slew of prerequisites. (On the pi - it functions fine on an amd64 distro with real mame)
I don't see that change any time soon.
regards