Wow, thought you were a troll when I clicked, that's not a question you see every day!
Doubt there's anyone here who could give you a definitive answer, but my gut feeling is that any caseworker will have reservations, particularly if you are considering adopting a baby or young child. They have a duty of care, and your fox, however well-domesticated, is one generation away from a wild animal which will inevitably cause concern. However, if you do your homework and are able to provide references and information from your local vet and the wildlife centre, you may very well be able to demonstrate that the risk is no higher than having a family dog. And, considering how essential love and patience are when fostering and adopting, you may even be able to turn the situation to your advantage.
Adoptive mum, former foster parent.