I did a boa breeding loan (the male was sent to breed with my female) and while my experience went well, it's not something I would recommend or that I would probably do again.
If you do it, just make sure to get everything in writing to cover EVERY possible thing that could happen. In addition to things Deborah mentioned, what if one of them dies?
I've heard stories of breeding loans going badly, friendships ending over greed and lies. Just be careful and make sure both parties are in full agreement.