You can find confirmation in the BE21.1 Licensing Guide on page 21:
The Backup Exec Server manages the backup environment (agents/options) and all tape/disk/cloud storage devices used for backup and recovery. Each Backup Exec environment requires at least one Backup Exec Server. Custom edition licensing: each Backup Exec Server license includes 1 Agent for Windows to protect the local Backup Exec Server.
Every Backup Exec Media server License comes with the agent for windows.
In his case if BE server is also acting as a file server. Then only
1 x BE Media Server License will be required.
Hope it helps !!!