I asked a similar question regarding a breeder placing a puppy in someone's home for the purpose of breeding when the puppy was older. The breeder would own the dog, until it produced 2-3 liters, and then the ownership of the dog would go to the "surrogate breeder." Here's the thread if you are interested.
http://www.yorkietalk.com/forums/bre...e-breeder.html By the way, I wouldn't describe this a mentoring relationship, sometimes the person taking the pup, didn't want to train to be a breeder, but was just offering a home, and this was a chance for them to get a "free" puppy.