Amen
pdsldl!
WOW! Freaky, because I just started writing a little about this in my own fic, I was very nervous about approaching it because religion is a hot-button topic. IMHO how
I view religion has nothing to do with the question.
My two cents... Vulcans at one time in their past were polytheistic with a pantheon with thousands of Gods. Any good TNG fanatic will tell you that because one of the very best episodes of the entire series focused on that. Also in TAS Spock mentioned he went out to the old temples to think, referring to "the gods of our forefathers."
We know that after Surak, "true believers" in his teachings kept belief in the
katra. They have temples, a form of clergy, that even said
prayers.
VOY stated that Tuvok's family went to a sacred temple to ask the Priestesses to pray for his safe return.They also keep and revere relics, as evidenced in ENT with the whole P'Jem disaster. Monks, Priestesses, High Masters, acolytes, all have prominent positions of authority in society. And they are set apart, from that society in many ways. Typical of many religious Orders.
Surak's teachings also teach that logic cannot explain everything. (For example it cannot explain why evil exists, but Vulcans believe in evil.) Thereby leaving a door open for believing something that could not be empirically understood.
Clearly these are a spiritual people. Just look at their marriage and death rituals. T'Pol's wedding is a prime example, the ceremony is far older than Surak. And it was far from a mere legal requirement.
(And there was that movie with Sybok) just saying...

Now does this mean that I think that the majority of Vulcans would believe in a supreme being. No. But some might logically conclude that there is no empirical evidence to say that such a being, beings, or "God" does not exist.
Therefore it would be illogical to categorically to deny the existence of a supreme being, beings, or force beyond ordinary comprehension.
Others might say the opposite, exactly because of a lack of empirical evidence.
According to Surak both would be correct, at least according to the teachings I've read. So I wouldn't say that Vulcans are categorically, atheist or agnostic.
PS Memory-Alpha is not coming up for me I'll reference the episodes I talked about later. Or someone with a better internet connection can check my facts with the site of their choice.