I never found out! The booking class is not displayed on NZ boarding passes, though it did say "Airpoints earned NIL".
But I was assured by BMI in writing before travel that I would earn 100% miles and they were manually credited as one lump sum. It would have been very annoying to not earn anything as the membership miles were needed! And flying UA in eco clearly would not have been an option. The NZ 747 (RIP!) was very comfortable, I dread to think how cramped the seating on the new 777 is.