If you don't have any media on it, and you don't intend on using it for storage, then just ignore it. MDs don't NEED to have a hard disk in them, so I would conclude that it is not necessary, apart from for storage (and as you say, 20 GB isn't going to get you very far).
The snapshots are like a bang-up-to-date DVD installation disk i.e. everything you need. Just follow the DVD installation instructions.
So what I hear you saying is, the core's only use for this drive would be for additional storage space. Otherwise, the core has no other use for the drives on the Media Directors.