Well, I know nothing about coding, so this is just an educated guess. It's probably possible, but it would have to be heavily modified to do so, and running it through Wii-Linux probably wouldn't be a good idea, as emulating takes more power than just running. I.e. The Wii has the harware to play games with GameCube graphics, but isn't powerful enough to actually emulate the GameCube. Poor example, as the Wii can play gameCube games lol, but that's only because it limits the hardware and shuts down Wii functions like the SD slot to make it think it's a GameCube.
And, yeah, you could easily use the Guitar Hero guitar.