Hill was and still is your typical shooting guard. Fairly good shooting, and he can occasionally drive to the basket and finish. He actually needs to improve his finishing around the basket. To be considered a combo guard you at least need to have decent handles (which Hill has), and at somewhat above average passing, which Hill simply does not have yet. His footwork also needs massive work, but he somewhat makes up for that with his wingspan. He might not be able to stay in front of his guy all the time, but he can reach in an poke balls away.
He could turn into a combo guard once he starts correcting some of those issues. Footwork and passing are key, IMO.
Mason, is a borderline shooting guard. He basically is a one trick pony. He could be a fairly good spot up shooter. He has terrible handles, his passing is below average, and his defense is lacking. Combo guard and Roger Mason really don't go in the same sentence.