I love Bulls, and yes I do not believe in taking aniamls from the wild....
What we do here, as we run a large reptile and amphibian rescue.
If we recieve native wildlife, they are completely isolated from any "exotics". They see a veterinarian immediatly and are treated for release. As stated above this may not always be possible. But with the right percautions and the right DVM TX it does work. I have released turtles with 3 legs that I have found a year to two years later in good health.
Something to say about any animal, ecspecially wild herps is they are tough. If your vet clears it for take off (even with being blind in one eye, if that is the issue) then so be it.
It's up to you. In my opinion WC is always better going back to the wild. Just my opinion with what I deal with every day. (even thou it may not be the popular vote).
I hope the Bull is ok. A vet could probably help you the best. But if he is moving, living, eating and pooing (and has been isolated completely) and has your Vet reccomendation for release. Then why not.There are always CB animals available. Just my opinion.
Rusty