I think it is possible, but you may only get $500 (from BMW financial), the other $500 is actually from the dealer so they may not apply it.
I am not sure whether it is correct, my guess is that, if you get the car from the dealer where you get the OL code, the dealer should apply $1000. If you give the dealer the OL code from other dealers, they may just apply $500 because you don’t attend their event.