Given the fact that he would essentially have to affect the other person's nervous system to cancel out the pain, I don't really see why he would need to experience pain himself as a drawback, unless it were some sort of side effect of using the power in general, rather than getting an analogue of the other person's pain. Having your sensory apparatus tampered with can already have its own nasty set of complications. Chiefly among which an incapability to feel pain might lead someone to ignore dangerous injuries, causing additional tear and damage. Not to mention the possibility of temporarily losing some dexterity or fine motor control in the process. But that's not really my place to say... <_<