Hades being Lily’s dad would certainly tie in the different story lines together. And if we go with Greek mythology, the gods definitely weren’t strangers to shape shifting — Zeus being especially prone to it of course, but Poseidon often showed up as a horse too. There’s no reason why Hades, being one of the three brothers, wouldn’t be able to shape shift too.
And that would be one more parallel to the show Lost Girl.
Yeah, there seems to be a lot of intersecting themes lately between the two shows. And Hades, of course, if he shows up on OUAT, is one.