It wouldn’t surprise me at all if this was true. Bill was once famously quoted as saying that she had “eaten more p**sy than I have.” And despite the lurid nature of its stories, National Enquirer usually has it right (e.g., they were on to John Edwards’ affair long before any other news outlet wanted to talk about it). They’ve only been successfully sued for libel once, AFAIK.
By itself, it wouldn’t be a factor in my vote, but it will for a lot of people. Particularly since it would be just one more thing she’s being secretive about.