Yes, it can be done:
- Use a separate RC object to create the surface of the green zones, set "Display->Viewport" to "Mesh" and turn off "Display->Render->VRay/Mental Ray shader". In this way, you get a mesh which can be used as Surface in Forest. Since only is needed a planar surface, the total number of faces should not be too high.
- For the rest of the road, use one o more RC objects with the default render mode, to get the benefits of the render shader.