Personally, I'm not worried about the guttata/emoryi crosses. Many people believe that corns and emoryis are actually the same species to begin with, calling emoryis Elapha guttata emoryi. (ie, emoryi is a subspecies.) Also, many people believe that Kisatchie corns are a natural population of corn and emoryi crosses. Since corns and emoryis will naturally breed with each other when they encounter each other in season, I feel pretty sure that there must be wild crosses where their territories meet or overlap, even if Kisatchies are not an example. Plus, their young are fertile.
Crosses with king snakes and milk snakes are another story altogether. Corns will not breed with these snakes without some form of trickery on the part of a human, and the offspring are normally infertile. These crosses are not in any way natural, and while I do not object to corn/emoryi crosses, I do not like the other hybrids. But that's just my opinion.