rsync itself has the ability to find differences between two directories and copy the differences.
copying files and creating users are two different things. You could combine both in one script but you don't need to if you have a rsync script already running.
i'm not a scripting guy either but there should be a way to output /etc/passwd from one system to a file then feed that back into adduser command. The following command will show you current users in the system without any other attributes that exist in /etc/passwd
cut -d ':' -s -f1 /etc/passwd
there should be a way to feed the ouput of the above command into adduser.
Guys ... need some help here?