The BMW clubs accepts all marquees just like the Audi clubs do, so you will be accepted.
As I stated above, the BMW club emphasizes smoothness over speed first, stating the speed will come with being smooth. First time I tracked with them (my first DE in fact) I felt I was being held back and didn't have that great an experience. I thought I would give them another shot with this event and I have to say, it was much better. I think it was just the instructor at my first DE. BMW has some good instructors with lots of race experience or track time. I learned a lot this 2nd event.
Logistically, BMW (at least the one I track with) is on the stricter side of rules. My club (BMW CCA NJ) does not allow suction cup mounted video cameras - they must be rigidly mounted (I used a C clamp mount) and the camera must then be tethered to the car using stainless steel wire in a length such that if lodged loose from the mount, the camera would not hit driver or passenger. Miss a class, you'll miss the track. Things like this is a turn off for me, but like I said, they're instruction this 2nd time around was really good. I plan on doing a DE with them in the beginning of June, so we'll see how that one turns out.
I would join - it's a nominal fee for a year and if they have lots of local events for you, it'll just give you that much more opportunity to track!