if the LPARs are on different servers with their own authentication mechanisms, yes it is required unless they can all authenticate through a centralized mechanism (i.e., NIS+ or LDAP) ...

if the LPARs are on 1 server, the user account requirement may be for each database ... but that would depend on how the databases are setup ... some might not require it ...

as for automation, there are a few out there that you can use --- we just use NIS+ where I work so I can't say too much for the 3rd party software ...