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I'd say the size of OCGW probably wouldn't be an issue for hornets (even though hornets are several centimetres long, they still benefit from eating many of them), but as smaller insects are for the most part incredibly fast, it would probably be difficult for the rather large, lumbering hornet (by insect standards) to catch any (if they were even suitable for hornets to eat). You'd need smaller, faster predators for that. I'm sure they exist, but I don't know much about insect-insect predation.
Oliver Schick-
Dryocosmos kuriphilus has a specific adaptation for rapidly infesting a stand of sweet chestnut;
it reproduces parthogenetically.
It is very likely the original infestation in Mad Bess Wood was from a solitary female.
Hornets, knowing there is always an easy meal at a bee hive, or from roadkill carrion, are unlikely to be actively hunting/patrolling a stand of sweet chestnut.The current hope for European sweet chestnut is the introduction of Torymus sinensis kamija.
mespilus
As far as I know OCGW are solitary and at 2-3mm pretty small, scarcely even a snack for a hornet. The only proven killer of OCGW is the Torymus sinensis Kamija mentioned above, which has been deployed in Italy, Spain & France, (within Europe).