depends if the body shop quotes for blending the paint into your fenders which imo is pointless... if it was the hood. MAYBE, but the rear bumper is off line with the trunk if looking from the back and it will look different because of shade and sun direction regardless of whether the colour is identical or not... imo, with the pearls and metallics that are in the paints today, even if the car came from factory, it will look different depending on how the sun hits the paint... and most shops will be able to match pretty damn close without having to blend.. if you are going the insurance route though and it is not your fault, you might as well get it done properly as you either don't have to pay for it anyways, or you pay a set deductible.
privately, i wouldn't really bother blending into fenders, just find a bodyshop with good equip and reputation for colour matching... and yes bring yoru bumpers in yourself and it will be quite a bit cheaper.. the rear is damn easy to take off