The fact that there is debate about whether String theory and Brane theory are scientific theories is good evidence that a reasonable debate can exist as to whether God theory is scientific. I have the site of at least one scientist who believes God theory is scientific.
http://www.thegodtheory.com/
Occam's razor is often paraphrased as "All things being equal, the simplest solution tends to be the best one."http://en.wikipedia.org/wiki/Occam's_Razor
In order to even apply Occam's razor, you need a non-God solution for the existence of the universe, which you don't have. Moreover, Occam's Razor also implies falsifiability, which again is debatably not a requirement of science.