This is my first instinct rather than anything I've used in play - Daredevil, when in use by a driver (not a Driver) provides +1 armor to the vehicle and the driver but these do not stack. So if damage blows through the vehicle to the driver it will be one less than the vehicle's normal armor suggests. On the other hand, if someone bypasses the vehicle armor entirely (shooting through an open window, shooting someone on a bike from behind), the driver's armor is directly boosted. At no time does the net effect of Daredevil reduce damage to the driver by 2.
Even more generally - unless its another PC attacking, you're not rolling anyway, you're deciding. Make sure that if the driver rushing into the action without hedging his bets that he takes 1-harm less.