my media server (which has been running for awhile now and never needed to use RAWS before)
Not quite sure how you managed that - BackupExec has required a RAWS serial to connect to a remote server since v9.0
but yes, if you have no RAWS serial installed, you cannot backup remote serverOS machines, even if the RAWS service is installed an running. DesktopOS machines need the RemoteAgent for full backups, but you do NOT need a RAWS serial installed on the media server to connect
In other words, do I need just one license for the media server and that's it?
RAWS is one serial per remote machine to be backed up (you can purchase multi-packs IIRC at a slightly lower cost per)