Just make sure they are equal in size. I tried to add some small peppermint shrimp, in with my large cleaner shrimps. The small peps didn't last a day, the cleaners ate them up like little snacks.
I now have 1 pep, and 1 cleaner about the same size they just stay away from each other, and occasionally the cleaner will chase the pep, but there isn't any fighting.