Eh, I think Guitar Hero just builds hand-eye coordination more than anything, which I suppose is helpful for reading sheet music and whatnot, and for just building dexterity in general.
Honestly I think the fact that you're playing to music is largely irrelevant. When you play guitar hero, you move according to what you see on the screen, not according to the sounds that you think should be produced as a result of your movements. The fact that you don't have to keep time or actually produce the sounds that you hear largely negates the benefits the game has to actually playing music, I think.
But I'm just guessing here.