On the good side, Graves is a "proven closer" who is 10 out of 12 in save opportunities this season. The bad news is that his ERA is 7.36, his K/BB ratio is 1:1.5 and he's looking at a possible suspension after possibly flipping the bird to the fans in Cincy after getting shelled yesterday. There's a lot more to the bad side than the good side, which only makes sense since Cincinnati wouldn't release him otherwise.
My feeling is to pass on him. A change of scenery might be good for him, but he'd be facing the same bats with us that he would in Cincinnati, and he'd have to make a couple of trips back to "the scene of the crime" in Southern Ohio, so to speak, which might not go well.
But even when Graves was at his peak, he wasn't very effective. The last time he held batters to under a .250 BA was 2000. He's always been more of a "guy who pitched the ninth" than a shut-down closer. Even with 41 saves last season, he didn't pitch that effectively and blew nine saves. I think we'd be better off going with Dempster and Borowski for now.