okay might not be a zoo.... but once in choicago, there was this pet store that had tomato frogs with i'm not sure the proper name it was a very small green tree snake. they got along for over a year untill the frogs didn't get enought to eat one night...
but then again they had over 10 cat of different age's that roamed free, and no not fixed.
in cali, there are a few side zoo's that keep smaller animal's together, kangaroo with an anteater, a verity of turtle's all in same inclosure, both land and water.
another one had ostrich, ardvark, and a house cat that acted like their mom.... hehe. it was cutie. my mom has photo's. donot know if she still has um... but i'lll check. might be a while though.