I heard something about somone integrating Renderman into blender.
It’s an old rendering export script for using BMRT shaders in external BMRT compliant render engines. I don’t know that it’s being maintained or whether you’ll get it to work with the current version of Blender. I think Little Cube was the last one working on it.
There are export scripts for aqsis and pixie and a few others that are current.