Okay, I just imported the OBJ with C4D's native function, not Riptide.  The CR2 loaded into D|S with it just fine, but no materials.  Then I tried Riptide, and the new CR2 loaded fine too, and with materials all in the right place.  So now I know it's something I did while modeling.  Maybe I can fix this by merging my modified OBJ with a freshly imported copy?