You make several suppositions, but have no evidence to back it up.
You write "And if Evans would leave it out of the manuscript Sudhalter had no way of knowing the incident happened, if it did, and made it up." How do you know that? Did you know that Sudhalter had been researching Bix for at least two decades before he wrote "Man and Legend"? Have you considered the possiblitiy that Sudhalter interviewed Ruth and got the information from her?
You write, "I don't think there is any information in Evans research verifying the Ruth pregnancy story." How do you know that? Have you seen/heard all of Evans collection of papers and tapes?
Speculation, especially when it ruins the reputation of dead individuals, is not appropriate.