Hannan's problem is he doesn't have the hockey IQ for it. He was successful by obstruction which is basically banned in the NHL now. His positioning is fairly sound, but he is not particularly good at predicting a players next move (like Vlasic is brilliant at). He's a poor skater, and fairly small. He just lacks the tools. I don't think Robinson is going to have much of an impact on him at this point aside from sheltering him.
Hannan might be marginally more effective in the playoffs ironically where obstruction is less penalized. However, hopefully he never see's a game in the playoffs anyway, so I just don't see the point of acquiring him.
The best we can hope for imo is that he retires after this season in teal. Even then, I'm hesitant about that as he chose to leave and made a point of jumping ship as fast as he could. I like to see the guys we draft and develop, like Clowe, retire in Teal if possible, but Hannan not so much. Don't dislike the guy, I just don't really care.