Wiimotes work fine with SNES as long as your game doesn't need more buttons. I haven't tried the nunchuck with it though so I can't answer.

The real problem though is that the Wii has a randomish lag on all input done. For example, I was playing Super Mario World, a game I can finish with all exits completed without dying once on the SNES or PC emulators. With the wiimote, it's almost impossible. You'll find yourself having all sorts of reaction problems... running off the edge of cliffs and that sort of thing. And because the lag isn't the same at all times, it's impossible to get used to and work around, unfortunately.