It did seem like the Master of Relics definitely had robes on... however from what few gameplay vids I saw, there were none to be found. And yeah I agree, Dark Angels are not themselves without Robes. Part of why I was mad at Space Marine was that the Dark Angels didn't have robes. And also I think in Dawn of War they had robes in MP but not in Last Stand.
I think it maybe depends on the type of Dark Angel that you are playing i suppose. To be fair, regular line troops are typically just green armor, while the sergeant may or may not have robes. But if you were a veteran or character or something, or a terminator, they definitely should have some kind of robes on at least part of their armor for sure. I guess once we start to see the actual 3D models we will know. I think all the stuff available in the Rogue Trader though will be more generic since it has to fit for all different Space Marine aesthetics, hence why they are not so Dark Angel looking.
I'm actually thinking of making one chaos char as a fallen captain yes yes I know it's heresy but man the art work is awesome for it.