Bill Clinton was a flawed man with a penchant for women other than his wife. It isn't inconceivable that perhaps he sought other women because Hillary has intimacy issues of some sort leading to frigidity. It isn't inconceivable that if the Juanita Broderick story was remotely accurate, that he may have had forced intercourse with his wife. In other words, I find the base claim plausible (though not likely).
The second claim about the rape being the source of Chelsea's birth I find lacking on the surface. Once again it is an anonymous source and could be crossed-wires between the source and Clinton (if the source actually exists and isnt flat out lieing).
However, the lack of evidence will always leave it unproven. Klein uses an anonymous source. Even if other claims the source makes can be validated, it doesn't mean the rape claim is.
On the surface I would say this claim is beyond skeptical inquiry unless some compelling evidence proves otherwise but I don't think it will. You have Bill, Hillary, and an anonymous source Clinton bragged about it to. If the source indeed exists, then Clinton obviously knows who the person is and can "out" them. The person would have been on Bermuda and close to the Clintons. I am sure a good reporter could deduct who it is from those clues alone or deduct that the source does not exist.