A Wii port of SDLMAME was publically released last night. To quote from the page linked above: Here I bring another distribution of wii-linux to play in our Wii, only if you have installed the Twilight Hack.
This time I bring you SDLMAME 0.125 (it's still hot =D) ported to the wii, which will let us play those old games from the years 80-90. I don't recommend using it with the Homebrew Channel, since there are hanging problems with wii-linux.
Furthermore, if you want to use this MAME version, you will have to be patient, since the loading times are big enough compared to PC. Even so, once you have gone through the phase of ROM loading, you can enjoy the games at a decent speed.