That's completely untrue outside of Guitar Hero 3. The problem I had with Guitar Hero 3 was that it lacked any real rhythm for a rhythm game.
I play guitar and that helped me pick up Guitar Hero (In its early stages) rather easily because I had a developed sense of rhythm. I mean, yeah, don't be expecting to pick up the game and master anything on hard, but actual guitar players or any musicians, really, are at an advantage, not a disadvantage.