While it's funny to me to think the demons of Pylea would be less into bestiality (I'm not even counting furry fetishes) than humans (making us the demons), I'm pretty sure Groo was said to have "cow's blood" by means they could test or measure, which implies he wasn't unique.
EDITED: Also, I'm remembering some parallel to slavery in the US South at one point being made. Slaves were seen as animals, not people, a type of simian (we all are simian, but back then they thought white people had souls, black people didn't, at least no more than cows, despite religion which I'd say was strategically used to get slaves to accept their position and obey their masters--and I vaguely recall a Bible story being interpreted to "explain where black people came from" in the Bible, a radical interpretation of the text, which some believed to this day, and implied they had less of a soul at best, EDIT 2:
Curse of Ham ), yet sexually abused regularly by whites. (That also went on in Nazi camps, though I recall hearing that one was disgusted by a female who abused Jews, not for the sexual abuse and accepting sexual favors to stay alive, but that she allowed Jews to touch her at all, which made the Nazi officer less inclined to be sexual with her.)
But at the same time, Fred is very inventive and cunning, and not just with contraptions...and with an unbroken spirit, she'd be underestimated all too easily by any who kept her as a slave. She could still fear it...but probably more in danger of it by other humans on Pylea.