just a quick word: in Poser we use the terms "shaders" and "materials" interchangeably because we don't have a native way of making materials that act sort of like templates.  VSS does, but those are called templates.  iirc, D|S has shaders like pwSurface presets, and HSS presets that define aspects of a material, while actual materials are specific (specific diffuse texture, specific bump map, etc.)

bagginsbill has created Matmatic for Poser, which enables scripted materials.  D|S has the Renderman Language for scripting shaders.  Poser does not have a way to script shaders.  if it did, bagginsbill would have eliminated the bugs in Poser's nodes ages ago. since you can script shaders in D|S you can probably script materials, but that's sort of like using Java to make a plain web page.  it's possible, but who would want to?  

the other thing that's really relevant is that you cannot mix shaders in D|S without Shader Mixer (and i'm not sure you can with it).  for instance, you can apply pwSurface to a material and get SSS, you can apply pwEffect to a material and get procedural freckles and veins, but you cannot apply both.  i'm guessing from the title and what little i know about  Shader Mixer that it will allow you to mix shaders, but i'm not sure how it would work with shaders not built with Shader Mixer.