I installed a trial version of ViaCAD Pro Mac, and the original STEP file imports with no obvious geometry defects. So, it does seem to appear that MOI might be having a little harder time with certain STEP files.
However, it did take substantially longer to import into ViaCAD than MOI. But that's not really critical.

The hyper-small scaling issue seems to persist, however. I tried performing a bevel on an edge, and found that I needed to use incredibly small (.001) radii for it to take. Just like what happens in MOI. So, it seems to be an issue on the NX designer's end.