Having hundreds or even tens of thousands of Unix accounts on a single system is not a problem in corporate or institutional environments since macOS integrates with LDAP and Active Directory via Open Directory.

I was able to log in to any of the Macs in the computer rooms on campus at my university using my regular Unix username and password.

UIDs go as high as 2 billion on macOS as well (they're signed 32 bit integers), which should fit even the largest institutions even without aliasing of local UIDs to directory server names.