I understand what you are talking about.
I have actually talked to someone about leasing one of my dogs.
But, it is with the intent of me sending him overseas for a few years then getting him back after he has been used for breeding an been able to have a wonderful show career over there.
As Pat and Lisa said, this is not common in the US.
Personally, I would want to know WHY they want two dogs. Training two Basenjis is NOT the same as training two Afghans or Beagles. I could see wanting to move to a less hairy breed, as she has uber amounts of hair in her place I am sure!
You have to think… do your puppy to be the one that gets the short end of the stuck and you get it back and have to "fix" what wasn't done in raising that you would have done? There are so many what-ifs to ponder to decide if this is really the route you want to go.
Also, you have to know that if she gets a male and a female, the likelihood of an accident is always there... so you would want to make sure if the other is a carrier, yours MUST be a clear, and vice versa. Better to be safe than sorry. You can email me off the boards if you want, I might be able to help you.