Sylvar aren't. It's explained in the Night Fae introduction that mortal souls get to choose a soul shape, i.e. one of those semi-translucent blue animal forms that are used for the Signature ability. Most don't seem to have any significant job in Ardenweald, either, though there are exceptions like Aliothe.
It's a bit notable that Night Fae are the only Covenant so far that isn't primarily made up of former mortals.