A couple of issues with the GI/FG translation…
When adding GI photon emission to a light, exponent and photon count get correctly passed, but energy is passed as a single float value (true to the nature of the single slider in the parameter), but mr is expecting distinct r g b values for the energy.
Global scene controls for GI and FG seem to be missing, one can add mi_finalgather/mi_globillum and mi_finalgathermode/mi_globillum mode to the object and that gets parsed. But, if added to the ROP, it doesn't add anything to the scene option block, so no GI or FG takes place. (The same .mi rendered with -finalgather on -globillum on command line flags renders as expected.)
RFE: Along with the last point, it'd be nice to have GUI controls for setting GI accuracy and radius, as well as finalgather accuracy, there don't appear to be any rendering parameters for those.

Also, while poking through the generated mi file, it looks like the options in the material instance blocks are being passed twice.
All this happens with 9.1.264, mr 3.6.51, both x86_64

Chris