And RAW with the SW FAQ:
Q. If the unit type that a Wolf Priest’s Oath of War
affects is declared to be Bikes, does the unit gain the
benefit against Jetbikes, and vice versa? (p35)
A. Yes, because Jetbikes is a subcategory of the ‘Bike’
My italics. RAW, the Dakkajet is BS 4 versus jetbikes and bikes, since abilities works vice versa.
Course, I doubt anyone would actually walk up to a game and claim that bonus, since I believe people are good and logical beings at heart.