You're all reading speculation and assuming its true. The Haunted variant will be just like any other helmet. Its like you don't have to buy anything if you want to buy the Mark V helmet first. The game won't say "You can't have the Mark V helmet because you haven't bought a totally unrelated helmet which you unlocked the first time you played the game" One thing I can say though, and this is not speculation, is that the skull has a tinted colour which changes with the "Visor Colour" which looks pretty cool.
Thing is Haunted is an extremely special effect, so therefore it would make sense for them to put extra limits on them. What makes you so sure that they wont?
haunted helmet CAN be bought from what I read on the halopedia, the haunted helmet is a variant of the pilot helmet, only seen and bought for 1 credit, once you buy every variant of every helmet. The description says "happy friggin haloween!" you need to be inheritor rank too. http://halo.wikia.com/wiki/Haunted_Helmet