Well if it is a pimped up BlackHawk then the tail and stealthy bits would be bolt on parts over the original skeleton and internal structures. You can see the tail rotor drive shaft in some of the photos. This more than likely runs along the same route as the parent machine whereas a NOTAR design would require a complete redesign of the tail section taking a long time (simulations, test flights etc) and money to develop.
Plus , we don't know how long these stealth helis have been operative . Afterall the Blackhawk and stealth technology have been around for the best part of 25 years as far as we know!