Today Aspyr, the company that typically ports games from other systems.. mostly PC to the Mac has announced Guitar Hero III for Mac and PC. That's a bit surprise but they did say that they where working on a new title that hadn't ever been on a Mac before and I guess this is it. The guitar that comes with the game is already compatible with PC or Mac because it's a USB device and I've seen people on the web getting it to work with no problems. So I don't think there should be any question about what peripherals it can support.
The Mac haters in the comments there are as ridiculous as usual. =\
The Mac haters in the comments there are as ridiculous as usual. =\