I'm going to disagree with this. In the wild, snakes are solitary and hatchlings disperse, reducing the instances of sibling pairings. People who breed for particular desired traits, like all the color morphs in corns, will breed closely related snakes to reach their goals. I see very little mentioned as to genetic problems...mostly limited to snakes kinked out of the egg, or stargazers.
I suggest that, as breeders work to more tightly refine certain traits, there will be a greater propensity to propagate damaged/defective genes as well. This is something we, as a community, might want to become more aware of and track. We go to great lengths to keep alive many hatchlings that would never make it in the wild... We need to be careful, before we end up with breeding lines overrun with genetic faults, like blind collies and epileptic golden retrievers.