Well, you DEFINITELY CAN use the intercom in DMC.UPDATE ON MY ISSUES:
I returned the Duo units and received the new set today. I also got a response from the support team, (pasted below). The Cardo Duo set actually worked right out of the box. I updated the firmware, tweeted the settings with the Cardo app and it's almost working properly. The only issue I've run across is that the "Hey Cardo" function works about one in ten tries. Not sure if a setting will help that. Will fiddle with it tomorrow.
Technical Support response: If I read it correctly it says: If you want to use your Goldwing on board audio functions, you can't use the intercom or Hey Cardo! WHAT??
As far as using the "Hey Cardo", I kind of understand not being able to use that. For example, using voice, you can tell Cardo to increase volume. When connected to the bike, you use the toggle switch on the left handlebar. The bike also has it's own phone call capabilities, so there would be a conflict with Cardo software if the Cardo was connected to the bike.
I've never used the Hey Cardo functions. Considering the Cardo (and other headsets) are used with a lot of bikes that do not have built in audio systems, I understand the reason why Cardo has functions that are not compatible with other bikes, like our GLs, HD tourers as well as BMW tourers.