Don't worry, I don't think sebrights are linked with lethal genes (thank goodness). The hen feathering is said, by some, to be linked with lower fertility in males, but I have not found this to be true. Some of my best breeding roosters are sebrights and they are full of themselves and most of the bantam chicks hatched are from them and not my other bantam breed roosters.
The hen feathering is caused by a dominant gene and only works in males because it is connected with the hormones of the male chicken, so young roosters and old roosters (with less hormones) may actually show male feathering. To my knowledge it is not linked with any health problems.
I have read, however, that sebrights bred to be small for showing and the like are more delicate and difficult to ship. In which case, certain strains may have weaker chicks that have trouble hatching.
I was worried about the low fertility I had read Sebrights had when I decided I wanted to try hatching some eggs. So far, he hasn't had any issues covering his hens.