There is no way you can take away from Reggie Bush just because he played against "west coast defenses" for most of the year. True, his team has an easier time rolling over the other teams with their overwhelming talent, but make no mistake about it, Reggie Bush is as good as advertised. You can judge a player and his talent regardless of what his team is doing, and Bush's speed, agility, reflexes and instincts are unparalleled. All you need to do is get him into an offense that he can develop with, and he will be a great player in the NFL.
There are always reasons that you can try to cut down on a player for, but make sure that any bad feelings towards USC don't cloud your judgement of Bush as a player.