We don't know that.
Doubtful they would got to the extent of having different finishing moves for every weapon then create a smithing system that doesn't allow the creation of uniques. My guess is that only uniques can be smithed.
well that depends on the way they make it. I mean, the way I read it was that the finishing moves were different with all weapon types (longsword, dagger, axe), not every single weapon in the game. still, that would be really awesome if it did it that way.
it would also give a reason to keep some of the weakest weapons in the game, if their finishers look cool