Also, Poser outputs RIB (Renderman Interface Bytestream) files natively with no shaders attached.

If you've got an editor to assign shaders / textures and you're using Renderman Pro Server (or Pixie or Aqsis or 3delight) then (a) you can bypass Maya altogether, (b) if you're adept at Poser's Material Room you're already halfway there and (c) Renderman Pro Server renders off the command line only for speed and efficiency that Poser Pro almost has. This workflow, though, is not for the meek.