Recover files from one volume to another on the same Drobo?
Drobo Support told me to NOT recover from one unmounted volume to another, but did not clarify why. It seems odd that there would be a potential of overwriting the first damaged volume, so I don't understand what's going on here. 

Fortunately I was able to find an external hard drive that I could recover the most critical files to using Data Rescue 3. (New purchase for $100).

Moral of the story: Buy a UPS for your Drobo. That may have prevented this problem.