Ayn Rand would fit more in line with an agnostic, professing to have no knowledge of the existence of God.
It seems to me that unless you are willing to believe that something can come from nothing, you must accept the existance of some sort of supernatural God. Once you've crossed this logical threshold, it's a matter of getting the nature of God right, which is tricky. I think anyone who is rational must be a gnostic (intentional space between the a and g) regarding God's existance, but I think everyone's knowledge about God's nature is incomplete.
Since you can not know or understand God through a completely rational process...
Can you know or understand any consciousness outside of your own through a completely rational process? It's a leap of faith just to believe something about your own brother's personality, much less God's. You can gain no knowledge of your brother's consiousness through any of your senses, so do choose to believe that you can know nothing about him? Is it magical or shamanistic to believe that a consciousness exists within his body?