That's correct. The first thing a Scout needs to do in grading a DB is determine his intelligence and instincts to defend the pass. The jump a College DB has to make in the NFL is considerable. He has to have the head and work ethic to be able to play his CB and/or Safety position effectively.
A DB may have the absolute desired height (say over 6'-0") or be shorter and possess an excellent vertical jump and sub 4.5 Sec. 40 speed but if he doesn't have the head for good ball defense skills he'll generally fail in the NFL He has to be able to turn up field quick with the receive and not get horribly beaten a lot to leave the open target.