My understanding on this, which may not be right, is that it is not as bad to do that with snakes as other animals, but it does have an effect. So where you can it is best not to interbreed them. I know with corn snakes, there has been quite a few problems with one of the newer morphs, Bloodred. They had to interbreed intensively to get this gene. It is better now that there are enough animals with it that they have started out crossing them. But there was problems like, to name just one, sudden death with no apparent cause. I'd be interested in what everyone else has to say on this though too.