You might want to view more of the Star Trek universe prior to declaring it "atheistic." While the subject doesn't come up often, when it does, Federation planets do have religion, faith and spirituality. There never been mention on the show of an atheist member world.
Very obviously Vulcans are people of faith. In the episode Hunters, a message from Tuvok's wife T'Pel included this; "My husband, we have been given the news that you are alive. Your children and I have asked the priests at the temple of Amonak to say prayers for your safe return."
In conversation with Neelix, Tuvok stated that the temple of Amonak is one of the most sacred
temples on Vulcan.
Being logical people, of course Vulcans have faith. Spock's family is polytheistic, which might be separate from Tuvok's families faith.
Kirk is a monotheist.
Deana Troi believes in the concept of destiny, the finality of events.
Worf and (less so) Torres embrace Klingon spiritualism.