I think you are real overthinking the "santa" thing. It is just a thing made up to accentuate Christmas. (I know God doesn't need accentuating). It is a pagan idea created in Germany, I think. It is not to usurp God's authority. On the contrary, it reinforces our Christmas traditions.
I do have a problem with people not knowing the true purpose of Christmas which is to celebrate the birth of Jesus Christ.
Jesus said that if someone is casting out demons in His name, that person is not against them(Him and His disciples). I think "santa" is harmless. If anything, Halloween with its witches, ghosts, and goblins, is a lot worse.