Nope. I've worked with people with many different, religious, spiritual and existential beliefs, including atheists and those with strong religious conviction.
You can believe anything and still get value out of this program. What is important is a willingness to explore your beliefs. Its important that you have an open mind, and willingness to recognize what is really true for you.
A belief in something larger than just you as an individual is important but its also something that we will cultivate together. That something larger could be God, it could also be ecosystems, or the universe.