I think we're having a bit of semantic confusion here over the meaning of "axiom." God's existence as an axiom is essential -- in the field of theology. According to Occham's Razor, it is not rational to insert God as an hypothesis into a scientific problem, when the problem can be resolved by natural explanations without the God hypothesis. And even in those numerous areas where science doesn't yet have a satisfying natural explanation, the God hypothesis isn't really an explanation -- it's just a technique for waving the problem away -- "No need to do any research here; God did it.".
It's essential in the field of the reality. The problem came when the material was declared to be the sum of everything.
Science cannot address the spiritual. If the spiritual is denied the most important part of existence is missing.
I agree with the posters who say invoking God's existence in a scientific theory is cheating. But to deny God's existence or imply that it is irrelevant makes science -- and everything else one would do -- ultimately pointless.