yes it does. Several photos in the shared library that I had not previously had in my library now have face data on them.How does the Shared Library interact with your personal Photos library facial recognition? Will the facial recognition (eventually) run on (any new to you) photos in the Shared Library?
Also, a nice feature is if it detects a duplicate it can combine a higher quality photo with meta data from the lower quality photo. For example my wife had a higher quality version of a photo, but I had added location and face meta data to my copy. It combined the two and kept her photo with my meta data.