Can it be used on huge wild animals if you get confronted? Like a black bear, gorilla, or the backyard dog? etc
To answer your question, no. BJJ is not the recommended solution to an attack.
To use your examples-
Black Bear- Just get out of the area without drawing a lot of attention to yourself. If you get the bear's attention try to make yourself as big as possible. If the bear decides to tangle with you then drop to the ground and cover up your vital organs and hope for the best.
Gorilla- Avoid eye contact and assume a non-threatening posture. Realize that if you tried to roll BJJ with a gorilla it could quite easily just pull your limbs off.
Backyard Dog- Stay standing, try to calm the animal, and back up trying to find a stick or something to swing at it if absolutely necessary. That is a great story and link but if that dog would have reversed from back control to guard that kid would have probably lost his life. Working on the ground with a dog trying to viciously attack you isn't the best recourse as you have given him much easier access to your neck and other vital areas.
Basically - No... Don't try BJJ on animals, save it for your siblings.