I think he helped unite any racial divisions by governing as the President, not the Black President. He was doing it already. That's what normalizing race relations looks like: you just govern, and try to govern well, regardless of what you look like.

Hyperpartisan opposition prevented a lot of legislative goals, but it didn't increase racial animosity, and the Obama administration itself was surprisingly recalcitrant to engage in hyperpartisanship itself (not that there were no instances, but for context you have to compare to the Republican anti-bipartisanship).