Depends on your definition of God, obviously, but from my definition it very certainly follows. For me (and for many philosophers) God is not an answer, but a question. I define God as the cause, and act of existence. What is the cause? That we do not know. But knowing that there is a result indicates that something causes it, and that something we call God.

Obviously, if you are talking about God as a deity, then no philosophical arguments of this nature apply. The only way to prove that there is a bearded man sitting on a cloud, casting lighting bolts and sculpting little people out of mud is to observe such a man or traces of his actions. I obviously don't believe in any deities.

Anyway, if you believe that the word God has too many connotations and cannot, to you, represent something as abstract as 'existence' or 'substance', then you are free to use a different word. However, when I think about your beliefs, I think about the ideas, and not the words. Just because our names for this thing differ does not mean that the ideas do.

PS: If you then proceed to argue that I am the only that uses this definition of God, you are empirically wrong. Many religions have at their root the belief that God (Brahman, YHVW, Tao) is a concept so large and complex that we cannot even come close to understanding a fraction of it. Certainly, they are not talking about a deity. As for philosophers... I am particularly fond of Spinoza, and this is exactly the God he describes.