Confirming...
Thanks for the quick feedback!
So to confirm: the actual mileage credit depends on the actual "operated by" carrier (Virgin in this case) not the airline who sells me the segment (bmi).
Right?
If so, then here's the related question: can I split the mileage credit so the three *A legs go to my *A account (United), and the fourth leg goes to the CO Onepass account?