I would not copy /etc/passwd and /etc/shadow to the Backup Server (BS)... it can be damaged if both servers are not exactly the same!! If no damage is made to the BS then, at least, the local root of BS would have the same password of the server.
Note that /etc/passwd contains:
1st column: user_name (user name of user or program)
2nd column: x (shadow passwd pointing to the encrypted pass in /etc/shadow)
3th column: user_id (by default in FC the users id starts on 500. So if you add the first user it will be 500, the 2nd 501, etc)
4th column: group_user_id (same as user_id)
5th column: name (name of user)
6th column: home_directory (obvious
7th column: bash_directory (points to the user bash location on users)
If you just add this to a new system, you would get a lots of errors because the home directory of local users is not created!
FC, by default, creates the home directory in /home when you add a new user, and adds the user info to /etc/passwd and encrypted user pass to /etc/shadow.
Plus, when you add a new user, FC will then copy to the user home directory the hidden configuration files located in /etc/skel/ (you can see them typing # ls -ali /etc/skel). So if no configuration files are created i think you will get more errors.
If you really want to make this you should copy, by hand (or making a script), only the line (in /etc/passwd and /etc/shadow) corresponding to user and add it to the backup server files, and then copy the hidden files in /etc/skel/ to the users home folder.
Just make sure that no users have the same number ID!!!
I think this will work but still not 100% sure of it
About samba, I guess there will be no problem (copy also smb.conf)