Backup to tape is working, so it sees my tape just fine. But I need a mountpoint for the tapedrive in dar:

That, combined with the end of the Dar2 miniguide I was given:
Create a mountpoint and setup the fstab entry
Then go to the dar2 menu item in the server-manager to set up the backup job(s).
Hope this helps.
...tells me that I need a mount point, i.e. /media/tape