Answer:
   
   A person's individual beliefs with respect to G-d are personal, and
   are not inspected by Reform. Even in traditional Judaism, there have
   been times when the greatest Jewish thinkers have questioned the
   existance of G-d. Judaism, in general, does not question one's belief;
   rather, it looks at one's adherance to the yoke of Mitzvah, as
   interpreted by the appropriate movement.
   
   However, the position of Reform with respect to Atheism is shown in
   its policy relating to accepting atheists for conversion. A
   [5]responsa in Jewish Year 5754
   ([6]http://www.ccarnet.org/cgi-bin/respdisp.pl?file=15&year=5754)
   stated:
   
     The important qualifying phrase is commitment to this religion.
     Reform Judaism is a religious movement, a community of faith
     dedicated to G-d. A ger must show a readiness to accept that faith
     in order to join our community. [...]
     
     [...]for Reform Judaism, a prospective convert had both to embrace
     the Jewish people and make a solemn declaration of faith in G-d,
     the G-d of our ancestors, as the one and only G-d. While many
     rabbis then and now insist on certain rituals and other obligations
     as incumbent upon the prospective convert (e.g. immersion,
     circumcision, a course of study, examinations, etc.), the sine qua
     non of conversion for Reform Judaism, as it is for all branches of
     Judaism, has always been faith in G-d. The centrality of G-d in the
     Reform conversion ceremony is verified by examination of the
     succession of rabbinic manuals published by the CCAR.
     
                                   [...]
                                      
     Some contend that since we find among the members of Reform
     congregations certain Jews who are avowed atheists or agnostics, we
     should not hesitate to accept a convert who falls into either
     category. It is true that some Jews experience crises of faith. We
     acknowledge the reality of the spiritual journey and struggle our
     brothers and sisters endure, and they remain part of us as long as
     they do not abandon our people or join another religion. However,
     that flexibility is reserved for those who are already "citizens,"
     who already belong. It is the nature of the conversion process that
     the convert must meet standards which, in practice, are not
     demanded of the already-Jewish: a program of Jewish study, required
     synagogue attendance, participation in synagogue and communal
     activities, and the like.
     
                                   [...]
                                      
     Reform Judaism is a religious movement of Jews dedicated to the
     covenant between G-d and the Jewish people. If we do not insist
     that the ger meet this fundamental standard and find herself ready
     to affirm the reality of G-d in Jewish religious life and
     experience, it would be a legitimate question whether we have any
     standards at all.