What a bizarre bunny trail that lead me down. I typically think of using diamonds as an abrasive. Using diamond for wear reduction on gears is completely counter-intuitive.Just because you don't know of it doesn't mean it doesn't exist.
Composite Diamond Coating, Wear Resistant Coating, EN-Diamond Plating for Metal Parts at the top of a quick search.
Now if this is a worthy application of such a coating? Probably not. But it does exist. The properties are not bad, just a different way to get to them. And it has the buzz words that marketing can roll with.