Is it possible to set up AD authentification from multiple domain servers?

We are currently using 'EPDM Login' and would like to switch to 'Windows login' to make up-keep easier, and since half the users cannot seem to remember more than one login at a time. The problem is that we are currently distributed across three sites, two domains, and four Archive servers. (Although all on one WAN).  I would like to pull AD user information from one group from each domain.  I would like to add both because 80% of our users belong to one domain, and the IT department will not add users not at that site, I can add the remaining users to the Domain server that I controll.    When I try to add the groups, in 'Archive Server Configuration'  it will only find the domain\group that the archive computer is currently a member of. 

If you choose Windows Login is it all or nothing?  If I cant combine AD servers, is there a way to use the main AD server and add a few non AD users to the list?

Somewhat related question:

I had been assuming that with EPDM Login, users and authentification was Vault level operation and being replicated to all of the Archive servers.  Since Login setup is part of the Archive Configuration does that imply that each Archive server can use a completely different user and permissions set?

Thanks,