Bayh doesn't have any negative ramifications on the left for Obama.
What!? This is a guy who gave away a Senate seat to the Republicans, cashed in, and then went to work for Fox News!
I don't think that the veep candidate will change anything for Obama. If the liberals love him (Obama), they won't care that Bayh is running with him. If anything, Bayh helps Obama in Indiana and other moderate states. I know some liberal who didn't like Joe Biden for some reason, but still voted for Obama because he was actually going to be the president. Not Biden. And in this case, it won't be Bayh.
I agree that Bayh is as big a DINO as there is in American politics right now, but I doubt it would have a major impact on Obama's vote total.