No need. I have dealt NDAs, contributing to writing them and have signed them. All the person has to do is prove undue influence, duress, unequal bargaining power for example. If enough people testify that the HR (including the head of HR) was acting as Sarver's personal interference and using that influence to make people feel that signing them was there only choice that is enough to bring the argument.
Straight from our HR site for officers: "At no point should you influence the acceptance of an NDA with your employees. Any perception of undue influence, coercion on signing the NDA could nullify the acceptance of that NDA and/or expose the company to future litigation. You must not have the appearance of influencing the employee's decision-making process."
I am no legal expert but I would assume that doesn't just apply to our officers but HR as well or anybody involved with the NDA process. You would have to one assume the previous head of HR is telling the truth and that HR was indeed using its influence to run interference for Sarver. That doesn't mean it's true or they will win but yet it appears to fit the criteria.