Hello,
Photo Mechanic Plus will read the metadata added by Lightroom as long as it has been saved to the image file or in an xmp sidecar file. By default, Lightroom will not save the metadata to the file so you will want to check the Catalog Settings' Metadata Tab. Make sure the box is checked to Automatically write changes into XMP. This could take a few minutes to complete. Next go to Lightroom's Metadata menu and select the Save Metadata to File option. Once this process is complete, you can use Photo Mechanic's Scan to Catalog feature from the Catalog menu, to add all of the files in the folder and sub folders, to the catalog.
regards,
--Bob