Obama was chosen because of Democratic racism?
On one level, your state may be right, but we'll talk about that in a moment.
For all practical purposes, you can say Obama was nominated despite Democratic racism. But had Hillary Clinton ended up winning the nomination it wouldn't have been "because" of racism. It would have been because more Democrats wanted her to be the nominee than wanted Barack Obama to be the nominee.
That's what is so tricky about "playing the race card." It can be very effective OR it can backfire on you. Certain politicians such as Jesse Jackson have made a career of racial victimhood. It's good for shaking down individual businesses and corporations for "contributions" to avoid future extortion, but it doesn't work very well when talking to voters over whose head you hold no club.
This brings us back to your statement. As I just said, playing the race card can be tricky. The Obama campaign has both been accused of doing it, and accused others of doing it. In the case of the North Carolina Democratic primary, Bill Clinton's sly remarks equating the campaign of Barack Obama with the campaign of Jesse Jackson 20 years earlier may very well have had an adverse effect on Hillary Clinton's campaign.