Each class has specific skills available that I know of. Somewhere I saw a picture of their control scheme for the warlock, L1 is a grenade, R1 in the Nova Bomb, and he can hold X (jump) to float higher/further. This implies that your guardian's 3 skills don't change. And bungie has said that race is for appearance alone. If there are racial abilities, my guess is that all racial abilities are available to all races, just at delayed rates.