This is story Ke$ha (or her PR team) concocted to garner media attention for her new album Warrior. Nothing gets people talking quite like racy/controversial/sexy soundbites. Sex with a ghost is all that and more. The only other celeb who's been bold enough to talk about supernatural sexual activity is Paz de la Huerta, who claims Elvis gave her an orgasm. And Paz, well, she's just … that's another post altogether.
Likelihood: High. This could be a total lie or a major exaggeration of something that really happened to her, but chances are, Ke$ha told this story just to get us to talk about it and in turn, BUY HER RECORD." Being as that I've spent a major portion of my day thinking about this, it's working.