White GSDs are off standard, which means that only irreputable breeders are breeding them. I have yet to see a breeder of white GSDs who is competing with their dogs in any venue and doing all appropriate health testing. White swiss shepherds are a breed, with their own (slightly different, but still different) standard, and therefore there is an outline to breed them to. With them being rarer, there are also fewer breeders that don't actually care about the breed, so most breeders are competing with their their dogs and doing appropriate health testing.