macOS Photos allows me to tag people that are in my photos. Is there anyway to access these tags via PHAssest or someother mechanism?
Access face tags
No, there is not an API to access people data in PhotoKit as of now.
Apple seems to be saving the face tag as EXIF, under prefix IIO. Where you can find x,y w, h, type, confidence level and face id which is a number. However the name of the person isn't stored. I assume, face id gets matched for a name in Photos app db.
There's no public API to do this, and Apple actually goes to specific lengths to prevent accessing face/person information using PhotoKit. Even using private APIs, access to that info is denied to third party apps, presumably due to security/privacy concerns. So, I wouldn't expect them to add this anytime in the foreseeable future.