I've been trying to get material style sheets working with Renderman so I can use them for material overrides between render passes. Does Renderman support this? If not, does anyone have a good setup for creating material overrides in RfH?

I don't think RenderMan supports Houdini's material style sheets. You can double-check on RMan forum:
https://renderman.pixar.com/forum/forumdisplay.php?s=&forumid=169 [renderman.pixar.com]

You can try using PrimVars to drive RMan' shaders and override the material parameters.