It depends what the drs put in the pump. They can regulate the maximum amount of medication that he has available within a given timeframe. He can't just hold the button down and get medication continually. He won't even have that kind.
There are different kinds of pumps. He would have one that would be implanted most likely. As long as the medication is controlled it should be safe. Do you know what drug they are wanting to put in the pump? That and the dose they're giving him would be my concern more than just the pump itself. Let us know. God bless.
I am not a dr. My statements are based on years of experience and related education. Consult with the professional of your choice regarding matters of concern.