Can I use my Wii Guitar Hero Guitar with Playstation 2 Guitar Hero?

no u cant cuz the playstation 2 guitar has to b plugged in but the wii one is cordless so there wouldn't be anywhere on the wii to plug in the playstation guitar. and also for the wii guitar u have to have a place to put the wii remomte in but there is no place for that one the PS2 guitar

Actually, it can be plugged in, the wii has 2 USB slots on the back. The Real question is: will it work?

It will not work because the guitars are console specific, not jst simple input devices. So the answer is no, the PS2 GH guitar will not work for the Wii