The Omega and most other inline muzzleloaders are not considered modern firearms and need no federal form to be bought or sold. The TC Encore is one of the few that is considered a firearm. This is because a modern centerfire barrel can be used with the Encore receiver.
Not by Federal standards; however, I wouldn't bet a thing when it comes to New York state or municipal requirements. In addition to the TC Encore you are required to use the 4473 for the Mossberg SSi-One, the NEF Huntsman and the first of the Savage in-line muzzleloaders. These are the ones I can think of at the moment.