I'm sure it has happened but I also expect it would be hell to take on Oracle in a legal fight. They'll have access to every email you ever sent, every online chat you've conducted via IM, or whatever, and I'd fully expect they'd trawl through each and every one looking for something to hang you with.
Not sure what grounds most people would have to sue on anyway. During my time there we were continuously made sign different disclaimers indemnifying Oracle for different things (ie: hearing problems as a result of spending time in labs). It may not seem the case now, but they're not dumb. They know how to cover themselves.
Tbh I was happy with my package. And getting Oracle out of my life completely, was an added bonus.