Breeding loans are risky because there's so much that could go wrong. Personally, I wouldn't do it. It's easier to just buy the snake you want.

To put it in perspective, most breeders do a 3 month quarantine. That happens before your snake even gets to meet his new lady friend. And when it's time to breed there's no guarantee the two snakes will lock. He might be away from you for an indefinite amount of time before he does, and even if there is a lock it doesn't guarantee eggs. Who is going to pay for your snake's food and care all the time he's gone? What happens if your snake gets sick or dies while he's in someone else's care? Or more likely, what if he just refuses to eat the entire time? A lot of male snakes do that while breeding. Who gets to decide when there's been too much breeding and he needs a rest?

I wouldn't go through all the trouble of putting a snake through quarantine just to breed him a few times and then give him back. I'll buy the snake I want, add him to my collection, and then I'll have all the time in the world to wait for him to lock with my girls. And if I decide to sell him later that's a whole lot better than paying a stud fee.