The question with Morillo isn't whether he is a traditional 4/PF. He isn't, but that is also completely irrelevant. BH wasn't either btw.
Thw question is whether he can competently guard the opponent's 4 or equivalent from time to time to spell Mirk without putting us at a huge disadvantage. I would guess the answer is not an absolute in either direction but is going to be matchup and situation dependent.
Mirk is going to play a lot of minutes. The backup minutes at that position will be under 10 mpg (maybe half that) and I imagine a portion of those will be double Ivisic lineups. When people say Morillo might get time at the 4, they're not talking about a lot of time.