Why do i need to import the Shaders required by the Crowd Characters in the Render Scene ?

When the render starts, the rendering engine translates the Maya rendering scene in its own file format (.vrscene for V-Ray, .ass for Arnold...). Thus, as shading assignment is simply done by attaching a Shading Group / Shader name to a Mesh, the required Shading Group / Shader nodes need to be translated as well in the rendering engine file format. To do so, those Shading Group / Shaders need to be imported in the scene and assigned to an active geometry (not hidden). If they are not assigned or assigned to an hidden geometry, the rendering engine optimizes the translation and ignores the nodes. To make sure your dummy geometry will be not visible at render time, you can deactivate its Primary Visibility or move it far for the camera frustum.

Hence, there's no need to save Shading Group / Shader along with the Geometry File (.fbx). The Geometry File is only used to compute geometry information (skinning, blendshapes, geometry caches...). Moreover most shaders (like custom renderer shaders) can not be saved in an Fbx file.

Thus the usual workflow is: