As there has been some question of the necessity of atheism in existentialism, one should point out that the atheist considers a godless universe and grapples with absurdity, issues of objective meaning, differently than the religious explaining their faith or constructing a specific notion of God. However, a strict atheism is not necessary to find absurdity in life, though it propels the question with a greater force in the absence of absolutes. In a lecture by Robert Solomon (somewhere on the internet, I cannot remember), the problem of evil is discussed as an example of absurdity within the belief in a benevolent God. Thus, a godless universe is not necessary to recognize absurdity, but the problem does not take on the specific dimensions of an atheistic perspective on objective meaning. Shortly, the problem of evil does not question the existence of God but rather the nature of his "plan," as evil exists in the world.
As for the question of freedom in the face of a divine "plan," such predetermination is not the same as being born into a certain facticity. One's facticity influences the choices one makes and allows for freedom only to the point that the specific facts of existence are not designed, that one's transcendence allows a person to choose to engage in a difficult, unusual action, something with a high coefficient of adversity, without corresponding to a preordained purpose for that person's actions. The problem is that our self-creation, our desire for freedom is cheapened, lessened, etc. when the specter of an omnipotent God enters the picture, when all our actions merely fill in the walls set for us by God. The idea of human freedom, in the robust atheistic sense provided by Sartre, Camus, etc., derives its power from the lack of a given nature in humans, the lack of a prepackaged self, the lack of a merely given freedom. As for Camus, the absence of the absolute allows humans a certain "increased availability" of action, able to live without appeal to divine purpose. The sole justification of human action comes from humanity, and self-creation thus takes on a greater importance in freedom for the atheist conception, an increased power and authenticity to oneself and others if that decision is not part of some divine plan but freely arrived at in a transitory body. Of course, this all arises from the human want for a seemingly boundless field of action: one cannot fail at scaling a mountain without freely choosing to attempt the action. In the presence of a plan, the outcome is already decided and known. "Degrees of freedom" are not what Sartre and Camus want: they give human freedom its proper power by attempting to live without appeal. Humans thus justify their own actions without recognizing a conscious giver and guarantor of freedom.