Based on experience, the rate is approximately 15%. Fleshformed and Powered Armor have already been confirmed as non-functional, suggesting that most, if not all, professional legendaries should be assumed to be incompatible. This also means naturals likely cannot have any bloodline.
Naturals *might* be able to get the Sorcery Legendaries at least, not sure about others.
From what I recall of H6 code, Sorcery doesn’t require being a supernatural. It merely requires the appropriate level of the arcane tree related, which I think requires being gifted.