It is thought that the vaulted skull was introduced using Polish. This was done several generations ago to increase the crest size. Now there are some lines that have vaulted or non-vaulted skulls. You can see it in full siblings. It is not well known how it is inherited. I have had vaulted skulls chicks pop up from two birds with non-vaulted skulls and vice a versa.I understand the vaulted skull can cause problems if they get hit but is it good or bad or indifferent if silkies have a vaulted skull?
Wasn't sure if that was a sign of something to be sure they had or didn't have or just to be careful.
In some lines, the vaulted skulls tend to female, but this is not reliable. So there does seem to be some element of sex-linking, but I believe it is more complicated than that.
With my last hatch of Silkies, there definitely was a relation between the vaulted skull and female gender, but then I also have some females with non-vaulted skulls from the same parents.
And, yes you are correct about them being more prone to head injuries with the vaulted skull. The skull has holes in it, much like a newborn baby. This is why any birds with vaulted skulls should not be kept with standard breeds or any aggressive breeds. They should also be kept in an environment where there is not anything they can hit their heads on if at all possible.

I attached a photo of two pullets that hatched last year. Full siblings that were sold to the same buyer, though one has a vaulted skull and one does not.
As you can the one with the vaulted skull has a much larger appearing crest.