As long as their brought up with the birds from being a kitten there should be no problems, just like certain dog breeds that cant be trusted around the birds unless brought up with them from the puppy stage.
Rab certainly buys the best so someone is getting a real bargain here. A hen I bought off him a few years ago bred a Fed winner last season from the channel (Talbenny) into Derry in the N/west of Ireland a real tough route to fly into.