I didn't read the entire thread, so others may have said this already... it depends.
Pardon my non-committal answer, but I think it depends on whether or not Calipari goes with the 3 guard look. If UK starts Fox, Briscoe, and Monk, I think 2 of the most important players on the team become Hawkins and Mulder. If you're starting 3 guards, you've got to have guys waiting in the wings to give them a breather and in the event of foul trouble.
From what I've read and even saw in that combine practice of Mulder, he's much improved over last season. His shooting is better. His defense is better. His athleticism has never really been in question.
Disclaimer: Calipari has always been known to play his best guys the most minutes, so it is possible, if a guy like Gabriel is playing so well that he must get on the floor, Calipari may switch to a bigger line-up when guards need breathers. He could put Willis at the 3 and then play Gabriel at the 4 or 5.
Edit: disclaimer #2, Mulder's defense. Off the bench, Calipari tends to favor the more defensive oriented player. If Mulder's defense is good enough, he'll get minutes.