My limited experience with DL lounges says it's all in the luck of whomever is greeting you. If your trip is all on one PNR, you have a chance. If not, probably no comp access for a domestic DL flyer. Doubt if the JFK Clubhouse would be available to you because you're not outbound on Virgin. But it may depend on what perks come with Virgin Gold. So, as with many aspects of travel, the message is: give it a try, you never know.