If the software doesn't manage UIDs internally then this is a recipe for disaster because keeping UIDs in sync is a PITA. It's a waste of time to do manually, but an even bigger waste of time to have to fight with the OS to get it right. If you're using NFS then you're screwed.
Usernames are one-for-one correlations with UID, so just don't allow users to personally owning files outside of their /home (they shouldn't according to FHS/LSB/POSIX/etc).
If the software doesn't manage UIDs internally then this is a recipe for disaster because keeping UIDs in sync is a PITA. It's a waste of time to do manually, but an even bigger waste of time to have to fight with the OS to get it right. If you're using NFS then you're screwed.