That feature is to restrict what FM files can be linked to the FM file you configure this in. As a way to prevent unauthorized "linking / referencing" between FM files.
The feature that you are looking for is External Authentication. This way you set up accounts in the OS of the server, or in an AD or OD if you have it. In your FM files you just need to create "external" group accounts, not individual user accounts. And the users can log in with just the one account as long as they belong to an OS/AD/OD group that is configured in each FM file.
Thanks for the info. Not exactly what I was hoping to hear but it cleaned up my confusion about the issue. Not sure if AD/OD is a solution here. The network team isn't likely to add the groups that I would need have created. I think the best that I could hope for would be one AD/OD group that allows Filemaker Pro access.
Take note that you can also just use accounts and groups in the OS of the server if AD or OD is not an option. Hard to imagine though that the network team would NOT cooperate. Typically they would jump all over this since it allws them to control access and consolidate security.