I've talked with someone who works with rehab/long term care of unreleasable poss's.
Cat food is a common staple. They also get lots of veggies, a bit of fruit, and some yogurt. They also try to get them a few mice a week too. I guess metabolic bone disease (which is related to calcium I believe) is pretty common for them. Sadly, even the best care gets them to 3-5 years. Lovely little guys though.
I walked up to a front porch with a bunch of kitties on that I pass by regularly. There were 4 cats and a possum just chilling in the cool autumn air. At least until my approach woke up the cats which then proceeded to chase the possum away.
I remember this lady in town who was a cat lady in an old mansion. There were like 5 cats in her front yard and this opossum walked up to the cats, they gave eachother a curious glance and then parted ways.
but yeah they can have other diseases and attack humans / pets. i know a lady that used to feed grizzly bears (!?!?) and was surprised when one killed her dog