MoI is using Rhino's 3DM file format. So, yes the files can be opened by both. But Rhino can support a lot of things which MoI does not. I believe MoI ignores the unreadable objects and property data, but leaves it remaining intact. So it can still be opened in Rhino once again without a problem. You might want to check with Michael if you plan to bounce back and forth between the two programs using same file.

jonah