Currently, if you import a prop (Create -> Prop) from an FBX file, CC4 will bring in the BaseColor and Normal maps if they are present in the corresponding .fbm directory. However, other common textures, such as Metallic and Roughness, are not imported.

It seems it should be fairly simple to support importing other common textures as part of the import process, saving users a lot of time manually dragging in textures after having imported the FBX.