Gravel trucks are the last trucks that should ever be hopping curbs though, even gentle ones. Gravel trucks already require many roads to be upgraded due to the weight and damage they do just to a flat surface. A truck carrying diapers and crackers won't mind so much, but when you got 50 tons of gravel then even a small 1 inch jump causes significant extra forces on both the road and the truck.
That road has been carrying gravel trucks for decades. The smart WSDOT engineers took into account the business with large trucks that is just a mile away when building this roundabout.
This roundabout is perfectly fine in practice.