The evangelical vote is just not in the south. That is an old held myth. There is a large percentage that reside in the Midwest, such as Ohio, Iowa and Wisconsin, all important electoral states. I can’t see a single southern state, outside of Florida, voting for Obama no matter who he picks or doesn’t pick for VP
Multiple southern states did in 2008. The issue isn't whether conservatives in these states will vote for Obama. They won't. The question is whether they will show up. That's what determines whether southern states stay in the red column.