Not really? Let's look at the material from the film, taken from the final version film transcript:

PETER: Well, okay. I found the name Zuul for you. The name Zuul refers to a demi-god worshipped around 6000 BC by the - what's that word?

DANA: Hittites.

PETER: Hittites, the Mesopotamians and the Sumerians.

DANA reading PETER's notes: Zuul was the minion of Gozer. What's Gozer?

PETER: Gozer was very big in Sumeria. Big guy.

And a little later scene:

LOUIS: I am the Keymaster! The Destructor will come, the Traveler! The Destroyer! Gatekeeper! approaches a horse on a wagon I am Vinz. Vinz Clortho, Keymaster of Gozer, Volguus Zildrohar, Lord of the Sebouillia. Are you the Gatekeeper?

And next scene:

LOUIS: Gozer the Traveler. He will come in one of the pre-chosen forms. During the rectification of the Vuldrini, the traveler came as a large and moving Torg! Then, during the third reconciliation of the last of the McKetrick supplicants, they chose a new form for him: that of a giant Slor! Many Shuvs and Zuuls knew what it was to be roasted in the depths of the Slor that day, I can tell you!

Pretty common apocalyptic cult fare; cyclical cleansing-of-the-world stuff. Sumerian religion wasn't cyclical in the sense of Hinduism (with the concept of Kali Yuga), or Aztec religion (with periodic new worlds), nor did it have a distinct eschatology like the Norse Ragnarok or Judeo-Christian or Islamic Armageddon. It did record at least one apocalypse in the 11th tablet of the Epic of Gilgamesh, and likewise they had a tradition of a god that dies and returns in Dumuzi, which occasions the descent of Inanna to the underworld. So your Gozer-worshipping cult isn't an impossibility, even if there isn't a strict historical basis for it. The specific details of Gozer being preceded by signs and portents, as well as a couple of folks to prepare the way, has (probably deliberate) parallels to Judeo-Christian stories about the coming of the Messiah. The cult led by Ivo Shandor has an historical parallel in the rising interest in Spiritualism, the occult, and Egyptology during the early 20th century, when groups like the Theosophists and the Hermetic Order of the Golden Dawn flourished.

Most of the names are fictional. There is no Gozer, Zuul, or Vinz Clortho in Hittite or Sumerian mythology; nor are Torgs or Slors known mythological creatures, and there are no known groups called the Sebouillia, Vuldrini, McKittrick Supplicants, Shuvs, or Zuuls. Tobin's Spirit Guide is not a real book (well, until recently). However, this doesn't mean everything is completely made up:

Dan Aykroyd says: "Gozer is based on several things. For one, there's a Gozer Chevrolet dealership in upstate New York. A little more to the point, though, is the fact that Gozer was a name that related to a documented haunting in England -- the one Poltergeist was based on, in fact. During this particular haunting, the name Gozer appeared mysteriously throughout the house, written on walls and things. So we figured we might as well take something that had been reported in the public domain as an actual occurrence and use it in the film as our main demon and supernatural force."

• Making Ghostbusters 97

The story Ackroyd was referencing is the Enfield Poltergeist, as recorded in This House is Haunted: The True Story of a Poltergeist (1980).