You need a Patent / Copyright attorney to decide if the O-U can stop it or not.
Depends for what.
To put an unauthorized OU on a package which is completely uncertified? I don’t need a lawyer for that.
To stop Hershey’s from doing it in the future? They just need to put it in the contract.
Maybe a third party repackager or a store can use it in a completely non-misleading way if the product really is certified.