A nip = a bite, same thing, just not minimized.
Your farrier should not have to discipline the horse because he bites, because the horse should not be biting him in the first place. I don't imagine that you'd be in a terrible hurry to pay his loss of income if he was unable to work for a few days due to a bite injury.
I highly doubt your farrier would care about possible head shy issues, I certainly wouldn't if someone elses horse was about to bite me. I'd whack the horse with my hand or whatever was in my hand at the time.