I don't know if they eat bats, but they do eat birds. Here is one on you tube eating a bird. They also eat bird eggs
and young in the nest. I have removed a few trying to get into my blue birds with young.
My brother's bat box on a tree had a squirrel living in it. It destroyed the baffles making a n opening to get in and reside. It is not a good idea to mount a bat box on a living tree according to what I have read.
Frank
http://www.youtube.com/watch?v=Ccl3KFZverk