If you have seen the mites then yes. They suck blood so ,they could have gotten so infested that he died , could have made him anemic from the blood loss. I would dust everyone and if you use the food grade sevin dust it might be ok on the hay but I would double check that to be sure. Im not sure what you use the hay for horses,cows, bedding??? You can still get those dusters that have a canister and you push and pull to dust.
