I understand, as he who responded said, that this suspension may not be "wrongful" in terms of the employer. However, could the young lady who surfaced these allegations be held accountable for "wrongfully" claiming this conversation to be "offensive" when her later actions reveal otherwise? (please view Wrongful Suspension? thread for details)
Additionally, what would you do if you were in my brother's situation at this point?

It would have been better if you had posted this as a response on your initial thread to keep all information together.

Without proof positive, and I do mean POSITIVE in big, bold black letters underlined, that the young lady deliberately falsified her complaint, it would be extremely foolish to attempt to take any action against her. Filing a sexual harassment complaint is protected under Federal law and the company could face serious repercussions if she filed a complaint with the EEOC that they retaliated against her for exercising a protected right.

If I were in your brothers shoes I would first, be exceedingly grateful that I was only suspended and not fired; second, accept the suspension as being appropriate for my own inappropriate behavior in telling off color jokes in the workplace; and third, keep my big mouth shut and stop using material that does not belong at work.