Are the A+ images exported at Amazon's required dimensions?

Yes. The images export at the pixel dimensions Amazon's A+ modules expect, so they upload into the A+ Content Manager cleanly and fill each module correctly — no resizing on your end, and no size-related rejections.

(Amazon can still reject A+ content for content reasons — prohibited claims, prices, and so on — which are about what's in the image, not its size. See Why does Amazon reject an A+ image?)