First off, you said it wasn't that deep. If so, eliminate the possibility that it didn't go through the color coat, such that the area could be sanded, and the hood re-cleared, with no color-matching being involved.

If you DO have to spray color, I think the shop that suggested painting the fenders to match the hood are full of ****. Here's why. If they re-spray the fenders, who's to say that the fenders will now not be a good match to the doors??? And if you're facing possible SLIGHT mis-match, you're FAR better off and the mismatch is far more hidden if the deviation occurs on the top of the car.

1. You would have to be standing directly in front of the car, or over the car, to have a chance of noticing.

2. Since the fenders meet the hood at an angle, and are curved, a slight color mis-match would largely be masked and imperceptable due to shadowing and differences in light reflection/refraction between the hood and fenders.

For these reasons, I would only touch the hood. THAT WAY, they can un-bolt the hood, and refinish it off the car, so your entire car doesn't wind up completely barfed up by overspray and compound and sanding dust, etc.etc....

When you have a slight color mis-match between a fender and a door, THEN you've got something that absolutely screams "REPAIR JOB", as the surfaces meet on the same plane and curve, and reflect light the same, making the ever-so-slightest variation jump out like black and white. And everyone notices, because the sides of your car is what is seen going down the road, in the parking lot, etc....

Sorry to hear of your misfortune, but at least they didn't run the key heavy down the side of the car. Coulda been a ton worse. Also, make sure the shop sands out the scratch, and builds up the entire area in primer, and then blocks smooth. Some shops will just sand a bit, and then skim-coat filler into the key scratch. Over time, the filler shrinks a bit, and you can percieve the faint key scratch under the paint....