At the point that Nikon refurbishes the camera and sells it directly to B & H, the grey market issue is no longer an issue. You get a 90-day USA warranty. After that how could Nikon refuse to service the camera if they provided a USA warranty on it? They would kill their refurbished business plus B & H would get a black eye as a reputable seller.
Good businesses can do stupid things, but the odds are the B & H won't leave a customer hanging out there. FWIW - I bought a refurbished D600 in January and couldn't be happier with the results.
"Red is gray and yellow white, but we decide which is right ....and which is an illusion"