Lightroom writes the crop metadata in the XMP metadata. If you examine the metadata of the file you'll probably see something like this:
crs:HasCrop="True"
crs:CropLeft="0.185980"
crs:CropTop="0.157018"
crs:CropRight="0.824514"
crs:CropBottom="0.769128"
crs:CropAngle="0.000000"
Lightroom's 5 color labels can be read by Photo Mechanic, as can its star ratings. If you're seeing crops in Photo Mechanic from Lightroom, you'll likely see star ratings too with no further configuration. If you don't see color labels that Lightroom adds, some configuration is sometimes needed.
Hope that helps.