I think because the Pro/AM is not an official class, you are not covered by the insurance. You generally need to be registered for the day in order to be covered.
In regards to the ABA, since the Pro/Am is not a real class, those riders don’t have to be reported to the ABA on the race report, so the ABA would not get some money for those riders. Not sure how the NBL system works regarding this type of stuff.