I phoned BD about that a few months ago, before they joined *A. I had a silver card at the time, and they confirmed that I could use any Red Carpet Club lounge. However, I tried to use the lounge at ORD and was denied access, as they had never seen a BD card, nor was it anywhere on their "accepted" list. Not a problem now though, but only with a gold card. The official line from BD however still says that all cards are valid there.
James - it's interesting that you say BD Gold is fairly tough to get; compared to either BA or EI, it is significantly easier. Particularly now that they are in *A - a single return trip to the US with United in economy will earn you almost a third of the required points to go from silver to gold.