I find this claim very difficult to believe. Ed Klein is pretty reliable, but I think he spices up his books. He's written extensively about Jackie Kennedy Onassis, most of it accurate, some of it preposterous.
Actually, I wouldn't be surprised if it's true. It would be bizarre behavior for normal persons, but Bubba and Butch are far from normal, IMHO. What if he does it often and she loves it, you know, like rough sex to the extreme?
Some say they are the most corrupt pair of individuals in the history of American politics. Could they also be the most weird?