GPA is as important as OAT scores. It seems to me that essays (where you can mention your experience) play a role only when academics (GPA and OAT) are on the borderline. Basically an application that has a chance should be rounded out. If your OAT is low, your GPA should be respectable and really strong essays/recommendation. In my case, I had a low GPA, but strong in everything else and I got in everywhere I applied.
Having a lot of experience is definately an asset. From what I know, rather what I've read on this forum, a low OAT score is usually balanced out with a high GPA. If the OAT is the only weak link in the application process you should be okay. If, however, you're OAT and GPA are weak, dynamite experience will probably get you some good consideration, though you may be sitting on the fence with this one. All the best, and never, ever, give up.