The only people I've heard use the term "sororstitute" are GDIs. I don't know why any woman would want to associate herself with prostitutes, but hey, people do all kinds of stuff that don't make sense.
I've never heard the term "fratdaddy" at all. The only thing that comes to mind when I hear that is Fry Daddy, which I wouldn't want to be associated with either if I were a guy.
What the hell is fratdaddy supposed to mean, anyway? It doesn't have any of the same negative connotation to it that "sororstitute" does.