"So... What happened to the last guy?"
SamAtt: I'd honestly ask yourself whether you're willing to walk away from an offer if what the guy says is bad.  If you are than talk with the guy.  If not than I wouldn't.Because he's going to be bitter.  So you're going to learn a lot of bad stuff about the place you're starting at.  That's a disadvantage in itself (because you might develop his prejudices and run his old enemies the wrong way).So if you aren't prepared to walk away than you're just torturing yourself with the information and making yourself less effective at a time when you need to be at your best (a.k.a. the beginning of your new job)