Rob doesn't need a jump-shot to be a 3rd star but he does need to be a lot more consistent and dependable.
Never sure what you're going to get from him. Impact or sleepwalking.
Edit: His defense, rebounding & team offense (passing, cutting, transition) are good enough to make him a high impact player without being a capable jumpshooter. That is why I do not think he needs a jumper to be a 3rd star.