No, he can't throw 90-100 pitches every 5 days-- he'll be fine by his next start but in-game fatigue will reduce his performance. He can start, but on the level of 70 pitches every 3rd day.
And the pitches don't work any differently in a starter vs. a closer role. His performance will likely be worse as a starter than as a closer given that stamina. Can you post him?