Maybe I'm missing something here, but you say you want to use UA to book a UA-codeshare flight operated by NH, but to credit the miles to your OZ account. If this is the case, I don't think UA crediting agreements with NH have anything to do with the miles you will accumulate on OZ. Indeed, the only crediting rules that will apply are OZ's -- and while they might credit a NH flight number, it would be unusual if they allowed you to credit a UA-codeshare number. But the final arbiter is OZ's rules, not UA's.