I think inbreeding is the same for all animals. My understanding its simply a matter of the fact that it tends to concentrate undesirable recessive traits.

So, let's say there is a mutation that is dominant. It will always show in a carrier and, unless it is fairly benign, will very likely prevent its successful breeding. On the other hand, recessive mutations are only seen by homozygous carriers. Since that is going to be far less likely in the wild, recessive mutations do not tend to be culled. For the most part they are silently passed around the gene pool. However, once you start in-breeding, the chances of two recessive genes matching up and becoming active are much better.

Consider that these desirable morphs are in fact what you might call "deformities" and many are quite undesirable to the wild BP. Likewise, most people carry recessive mutations that just don't tend to show up - until they start in-breeding. Its the same thing with dogs. "Pure-bred" is a term that refers to a process of breeding that isolates a particular set of genes. During that process, undesirable genes are isolated along with those that the breeder is interested it. That is why certain breeds of dogs tend to have genetic health problems like blindness, etc.

So, with snakes, I would guess that the risks from in-breeding are similar and that it would always be preferable to isolate recessive traits by breeding between lines rather than within one. But, what I don't know, is how many genetics defects snakes really tend to have beyond the color morphs. Perhaps their makeup is pretty simple and they are fairly resilient to in-breeding.