The default iSCSI configuration of the DroboPro is marked "Automatically configure (Default)" in the Drobo Dashboard utility. This doesn't mean DHCP but instead resorts to using Zeroconf addresses (169.254.0.0/16). In a point-to-point configuration such as yours, you have two choices:
1) Leave the Drobo Pro in the "Default" network configuration and configure your network adapter for DHCP. The DHCP client in Windows will eventually timeout and you should receive a 169.254.X.X address for the network adapter. The Drobo Dashboard utility should eventually find the DroboPro (could take a few minutes) and make an iSCSI connection.
2) Connect the DroboPro to your Windows system via USB and setup a static IP address on the DroboPro. Then, statically configure you second network adapter for an IP address within the same subnet. Restart your Windows system, remove the USB cable, and wait patiently for the Drobo Dashboard to find your DroboPro and make an iSCSI connection.
The benefit of the latter configuration is that you lose the "limited or no connectivity" message for your NIC. If you're impatient and don't want to wait for Drobo Dashboard to find you DroboPro then you can setup the connection through the MS iSCSI Initiator in the control panel when you're using static IP addresses.