I'm curious as to how you'd be able to sue the gang of 88? I can potentially see suing Duke for the suspensions but it seems to me the gang of 88, though disgusting human beings, were simply exercising their rights to free speech.
You can sue anyone for anything.
But for a serious answer, and subject to the disclaimer that I'm not a North Carolina attorney, I'd start with defamation and false light invasion of privacy, and then would throw in some conspiracy - you would need to research NC law to see exactly how to frame those allegations.
Yes, the 'listening statement' ad is highly inarticulate, but the attempt to tar the defendants as racists should be actionable. And, of course, some faculty members have gone far beyond the group statement: http://www.dukenews.duke.edu/mmedia/features/lacrosse_incident/lange_baker.html