It was pointless for the episode. The whole episodes revolved around the Doctor interacting with a snooty EMH Mk 2 to save a ship from Romulans. It was a lot of fun and comedy. It didn't need DS9 at all. I'm kinda baffled by Admiralscreed marking it down just because its an episode set partially back in the alpha/beta quadrant and it doesn't feature anyone from DS9. Besides, DS9 was a long way away from where the Prometheus was being tested.