This may not be relevant for two reasons
1)it's been a very long time and many brain cells ago
2) same as #1
Many years ago, if I remember correctly, older Unix sysetms System III just had /etc/passwd as the main file that was used to set up user accounts. Then somewhere around system V and above the use of /etc/shadow came into being.
There was still a /etc/password file but the shadow now had all of the information that was pertinent to specifiying the users account status and password.
Back then, there wasn't any kind of configuration that was necessary, it was just available and working in the release.
The reasoning for the shadow file is a dim and distant memory, but I seem to remember that it added some extra layer of security. That could be all wrong but that's what I seem to remember about the situation. I don't remember having any problems with using the shadow password stuff either.
Sysadm stuff worked just like it did on the earlier versions.