I am doing that right now. I have one of mine leased out and she will come back in foal. I think it is a good way to do things these days. This is a great way to mix up your lines and not have to buy a mare to do that..
You have to make sure when you lease one of yours or lease one for yourself that you have a contract and legal breed association lease signed. You never know what can happen and it needs to all be spelled out in a contract. Such as if the mare dies or gets injured, vet care, etc. I leased Chad's mom to a gal in CA. I had her carry insurance on her. She could not get her in foal..
When she brought her back I bred her to a stallion that had to be shipped counter to counter and got her right in foal. Then again this year when I bred her to a horse in Kansas.. first shippment and right in foal again. I think the gal who leased her even left her at the vets to get her bred..
Anyway, I think I still have the contract. If you want to look at it and use it in your lease email me and I will send it to you..