You mean other then things such as flying it on Government buildings, for political events, as a standard for the military, for identifying NZ ships, and for state funerals? All things we really want to have associated with sport....
No, marketing emblems and the flag are not required to be the same, and I'd suggest again it's a bad idea. Marketing emblems are generally trademarked by the organisation doing the marketing. Besides, we use the Kiwi silhouette in a lot of NZ marketing too, it's probably just as recognisable as an NZ emblem as the fern is. I wouldn't be going for that either. Reality shows that very few countries have their nation emblems, plant or animal, on their flags. There is no need for us to do it either.
Yeah because the story of our shared heritage of British colonists and the Pacific peoples who used the stars to guide them coming together to live in this land is so much a worse story to tell kids about than, oh, we got from a rugby team.
Actually I'd be highly surprised if they didn't fight it. Organisations spend a lot of time and money investing into their brands, and losing control of them means losing all of that hard work. If the black flag with silver fern was adopted, the NZRFU would lose total control of their trademark. Imagine just the loss of income in gear sales when rivals started selling black rugby jerseys and other merchandising all emblazoned with the "New Zealand Flag".