If you're using NFS mounts, user IDs should be synchronized across all servers. This is typically done via LDAP or NIS, but you can do it via manually managed gids and uids as well.
This is all great... if you remember.
If you forget when you're adding a new user, you can still fix it:
usermod -u UID USERNAME
groupmod -g NEWGID OLDGID
On RHEL, you may need to use /usr/sbin/usermod and /usr/sbin/groupmod