I've just finished reading a very interesting blog post that discusses the scientific approach to gauging the interaction between rescued animals and people who are somehow in need of rescue themselves. It includes a really great passage about a prison program through which inmates work with animals who were rescued from overcrowded shelters, where they had been slated for euthanasia.
Juliette Reith, in her blog post True Animal Rescue: How Pets Save Us covers a lot of ground relevant to both physically challenged pets and emotionally challenged people. I strongly encourage you to take the few minutes required to read it. If nothing else, it will make you feel validated about things you've always believed about the healing power of critters.