To my knowledge, all the hyperscalars have their own racks, usually several generations of them, and ODMs make custom boards for all of them. None of the hyperscalers is buying standard off the shelf because their infrastructure is not off the shelf, and they have no regrets. I have studied Meta's choices and they make perfect sense for their use mix, which has shown a high level of co-design optimization between product needs, software, and hardware.
All ODMs want those businesses. Any one contract for a hyperscaler dwarfs the size of shipments of "standard" designs. When they win such a contract, the "A" team is on execution. The insights they learn from seeing the future in the new things hyperscalers do is gold.