Can a Netgear ReadyNAS be used as a Time Machine Backup Destination? We have a NAS (a Netgear ReadyNAS NV+) in our office with tons of free space that we'd like to connect to our Mac Mini Server, mount as a disk and then use as a Time Machine Backup Destination. 

This way the clients back up to the Mac Mini, while the data is actually saved to the NAS behind the scenes.

Problem is that I can't figure out how to make Server.app show anything other than the two built in drives. 

I've tried mounting a share from the NAS with both SMB and AFP (it shows up fine in Finder). Maybe there's a way to use a "local" destination and NFS that directory? 

Or is this not even possible?
To use the Time Machine Server function in Lion Server, you'll need to use a built in drive. As long as the NAS is able to be seen on your network, you should be able to use it as a Time Machine backup destination on each client Mac. While you won't be able to configure this for all machines at once in WorkGroup Manager, you should still be able to set up each client Mac to back up to the NAS.