Gutters above Garage Door on slanted driveway - is it necessary?
Water pouring off the roof will be an annoyance when you're driving or walking in/out of the garage door.
Water pouring off the roof will damage the concrete (take a look at the Grand Canyon if you're not convinced what water can do).
Despite the slope, water will splash, puddle and eventually get its way into your garage.

Yes, you should go ahead and get the gutters installed above the garage door. For the small additional cost, it's well worth it, IMHO.