I don't know for sure, but I would say no, the 484th did not participate in the D-Day invasion. My reason for saying so is that Normandy was way too far for the Fifteenth Air Force. It was one thing to fly to southern France to support Patton when he invaded there, but I don't think they could have made it to Normandy and back.
According to my Father's war log, his group the 49th with the 825 squandron of the 484th flew into the Xenia Oil Refineries which were in Ploesti. This occurred on D-day but they were not a part of the invasion squad. Hope that helps.