I have cleaned feed dogs so gunked with oil and lint that they felt dull. Feed dogs wouldn't dull appreciably with most fabrics, although they could dull if the machine was run a long time with the foot down on the dogs.
Scrape the grooves with a pin, point of a seam ripper, or a dental pik type tool. If you get gunk, rove the feed dogs and soak in rubbing alcohol to loosen the debris.