There is no reason Ober should be on any type innings limit...Other than an unproven theory with little or no supporting factual evidence.
Let the man pitch. He might get hurt. Pitchers get hurt all the time. If he gets hurt, he misses time, which is exactly what happens if he misses time because he was held out. He also might be just fine, and NOT miss time.
A six man rotation is a poor idea, for all the logical reasons listed above.