I give treats. But I'd never allow any nipping. I am not a treat dispenser. I give treats when I feel like it. I think you have to be careful about giving a treat every time a certain event occurs. For example, I'd not give a treat every time I groom or every time a horse does a requested task.
You know, I am the alpha horse when I'm working with the horse. You don't nip the alpha and expect to get away with it.