Perhaps. However you have to realize that by "using the animal" they get funding, the funding goes towards the research that is done on the animals at these places, which is usually behind the scenes. Also they usually release "when their done" or feel the animal has to go back.
Besides these animals get to stay in an environment without predators, food is abundant, and while they don't exactly have the sense to know "nothing is wrong" most likely they'll survive longer than they would in the wild.