I'm currently reading Anthony Marsh's excellent book, "Fourteen Years in the African Bush". At one point he relates meeting a person who had spent time with W.D.M. (Karamojo) Bell. Bell was well-known for being an exceptional rifle shot, with some reports that he was so good he was able to wingshoot birds with his rifle. Marsh says that the person who knew Bell said that he drove everyone nuts constantly dryfiring his rifle.
There's not a way to prove a cause and effect relationship, but it seems clear that a lot of dryfiring doesnt hurt one's marksmanship abilities.