I think that the ghost in "The Queen of Spades" is real within the story. Given that Hermann does not have any gulit or regret over the death of the countess the ghost cannot be a mainfestation of the guilt or regret that he feels. Therefor the ghost is real. The Countess also gets revenge upon Hermann by making him lose in his final game and the later causing him to go insane. If the countess's ghost was not real the first two cards would not have been the right ones.