I've really only watched Stargate: Atlantis, so I don't know if this is brought up in SG1 or Universe.
Are the Ancients ever described as being religious, or worshipping any deities?
The ancient Alterans didn't have a religious faith but they did worship science. That was the entire crux of their argument with the forces of the Ori who eventually forced them out of their home galaxy.
ALTERAN WOMAN TWO: We believe in the systematic understanding of the physical world through observation and experimentation, through argument and debate, but, most of all, freedom of will. I will not compromise the fundamental tenets of my devotion in order to preserve it.
Eventually both branches of the Alteran people ascended. The Alterans in the Milky Way became the Ancients and the Ori founded their own religion.