You cannot pass a static model into the render component, because the render component is what loads the model. Unless you exposed model loading to something outside of the render component, which defeats the purpose. There is no importance to having a model for rendering without a render component.
Terrain and Skydomes are both models. If terrain doesn't have a render component, that is because it hasn't been converted to do so. It certainly should be made to have one. The only reason I can imagine that is doesn't have a render component is due to the fact that each quad-tree section would have its own render chunk, and possibly then each quad-tree section would need its own render component (which doesn't work because you can not have two of the same component on a single entity).
There is no reason I can think of that sky cannot just be treated as another model, and thus us the render component with the path of the dome passed in. Of course it may need a different shader, but I think that material can be setup to handle that.
