Haven't looked or tried but the next time I'm on, I'll look around. We came across a Rhino hiding in one of the air ducts above the container area tonight. We were gathering in the room atop the scaffolding where the machine thing takes the drill to the hive. In that area, look out toward the containers then up and to your right.
It may have been a glitch. We thought it was at first. However, we all shot at it and, sure enough, killed a Rhino that was just sitting there. Didn't get anything for it. Don't know if it was part of an easter egg or just a glitch.