According to CNN's exit polls. Obama won 83% of Clinton voters nationwide and only 68% of Clinton voters in Arkansas. I don't see how you can look at those numbers and say the primary was not a major factor in the huge swing we saw in this state.
I believe that Clinton was a factor in 2008, but I'm skeptical that the 2008 Democratic primary in Arkansas was enough to deliver every statewide office, the legislature, and the entire congressional delegation, to the GOP in six short years without any indication of them swinging back in the near future. More was definitely at play here.
It is interesting, though. If you take the early Clinton-McCain polls at face value, this could have been what the battlefield resembled in 2008:
