People do it all the time, however it doesn't make it any less likely that you'll get deformities. Inbreeding decreases the genetic diversity in the gene pool, which is why it is good to bring new blood into your breeding projects on occasion. Just like breeding a het albino to a het albino can get you an albino, breeding two siblings that may share a harmful mutation will mean that you are more likely to produce a snake with a deformity. It is a crap shoot but most people do it with no ill effect.