Can I get ownship detection when my Stratus 2/2S is plugged into the Stratus ESG?

Yes. If you have ForeFlight version 8.3 or newer, ownship information is provided via the USB power/serial port cable that connects the ESG to the Stratus 2/2S. You will also want to have the antenna cable plugged into the Stratus 2/2S if available to you.