Hi silverwoods, they are probably either mesh objects or block instances. You'd be able to tell by selecting them and using the "What" command in Rhino.

For mesh objects there isn't really a good way to bring those into MoI because MoI does not work with meshes for modeling.

For block instances you could use the ExplodeBlock command in Rhino to convert the block instances into regular objects and then MoI would be able to see them.

- Michael