Drobo can be direct or network attached so may depend on your model. Network attached can be connected directly to the hub. If it's direct connect type then I'm not sure about USB. Give it a go as you won't break anything.
The drobo dashboard should find your unit anywhere on your LAN. If you want to do anything fancy with it a fixed IP would be a good idea either outside of your DHCP pool range or reserve an address within the hub admin page. Depending on your your unit there may be more than one network connection too so reserve each MAC address that you will use.