I have a Rainbow shark and a 18 Cories on the bottom of my tank without issue. The Rainbow shark is fairly private and likes his hollow log. I am sure the cories have learned to stay out of the log but otherwise, he is not an issue with them. They are in a 4 foot long tank 60 gallon.
“The greatness of a nation and its moral progress can be judged by the way its animals are treated” Mahatma Gandhi