The statements about sib x sib = parent x offspring are true as far as the odds, but I believe that it really ends up being random. It depends on where the bad genes are (if there are any), and we don't know that in advance.

If you have a male snake that has some genetics you want to work with, you could breed him to his daughters. If he also happens to have some bad genes, that could end up being a bad situation, and breeding his sons to his daughters (brother to sister) would be better. But, on the flip side, maybe the dad is fine genetically, but the normal female you bred him with carried a bad gene, then breeding back to the father would be safe, but the brother to sister might result in deformed offspring.

The safest thing might be to breed the male to at least 2 different females, then bred half-siblings to each other. However, that still doesn't guarantee that you won't end up with a defect popping up.

It does seem that doing a moderate amount of line breeding or inbreeding usually does not turn up any issues. I've seen a lot of people say it appears to be safer with reptiles, but in actuality I know a lot of line breeding and inbreeding has been done with dog breeds and lots of other domesticated animals, and while genetic defects do turn up sometimes, it is relatively rare in comparison to the amount of inbreeding that gets done. So I'm not sure about "safer" with reptiles, but it certainly appears safe enough when done in moderation.