the reason that the offspring would be sterile is because of a nonmatch in the number of chromosomes but even in that there is still possibilities of non sterile offspring take mules for instance there are a few reported cases of nonsterile mules only females though and when mated to a male horse ( since there is no possibility of a nonsterile male mule) will produce a 100% horse foal.. so given that even if you were lucky enough to get some offspring from your hybrids that werent sterile chances are that if you mated it you would only be able to mate it back to one species or the other that was its parents successfully and end up with a 100% in that given direction... (did that make any sense? lol) but then again that is with mammals and we are talking about reptiles here.....