HI Shannon,
Can't help you with the DC question. I can tell you that the Blue Lagoon Dolphin swim was incredible. Blue Lagoon will ask if anyone wants to upgrade to the swim if they have openings.
We did the Dolphin swim in St. Maarten/Anguilla in 2004 and the Blue Lagoon in Feb. 2005. Blue Lagoon is beautiful and the dolphin swim was great. While you are waiting for your turn, BL staffers give a very educational talk about dolphins and their habitate. My 11 yr old remembers quite a bit from her talk. They spoke about the perils humans pose to dolphins and there was a photo of what has been done to dolphins in the past. The photo was graphic, but it made a point with everyone there. There were 2 dolphins with us during our session in the water. We fed the dolphins, danced with them, hugged them and kissed them. The toe push was beyond words. Did you see Rob and Amber's wedding (Survivor Rob/Amazing Race Rob & Amber)? Amber went to the Blue Lagoon and they showed some of what they do with you and the dolphins.
Maybe someone else can answer your Discovery Cove question.
Poconoboatniks