Inside of the Parts Shader should be multiple Object Parts (gray node color) with attached Default Shaders. If you're not seeing these then it's quite possible your exported OBJ doesn't have texturing info included with it. It could be that no .mtl is being exported by Blender (it should be able to do this, so check export options), or that the .mtl is blank or not correctly formatted. If no UVs are setup in Blender and you intend to texture it entirely using procedurals then just connect your "snow" node(s) directly to the Surface Shader input of the Object node.
- Oshyan