Supreme King Gate Zero's role/s in a Dark Magician deck?
As your answer indicates that you suspect:

To Improve The Chance That Dark Magician Is Summoned On Turn 1

In the deck/article you've linked, the purpose of Gate Zero is to be used in tandem with Supreme King Dragon Darkwurm and Destrudo the Lost Dragon's Frisson to summon Odd-Eyes Meteorburst Dragon, and subsequently Ebon Illusion Magician. This inclusion of Darkwurm/Gate Zero exists solely to achieve this opening move, so that Dark Magician can more consistently exist on the field on Turn 1.

As the name sort of implies, the "Dark Magician" deck tends to prefer having "Dark Magician" in play; so it is quite desirable to optimize the likelihood of him entering play as early as possible. Gate Zero is a means to this end.

The other capabilities (although, certainly not the intended purpose) of Gate Zero are to summon Dark Magician the Dragon Knight and destroy it in a seldom-occurring pinch, or to set up a pendulum scale from 0 to 5 with Darkwurm, allowing the player to Pendulum Summon any of Maxx "C", Magician's Rod, and/or Flamvell Guard. And as you've noted, of course, it is a legal card to banish via Allure of Darkness.