Read the book, theory is possible. What guy lives for 33 years and doesn't get busy at least once?
I have, actually, and I think that anyone who takes it seriously probably has a full assortment of different kinds of tinfoil hats for all occasions.
And anyways, the idea of "what guy lives for 33 years and doesn't get busy at least once" is a valid argument if you start from the standpoint that it's ridiculous to think that JC was anything but a man. We know, for a fact, that in the Dresden Files he's at LEAST a scion of TWG, and most likely an aspect of him.
Jim bases his world off of myths, folklore, and world religion; he doesn't base it off of another fiction author's work. So there'd really be no reason, at all, to have to link Butters to someone who would have immense metaphysical implications if they DID have offspring, when he would already be linked to King David and King Solomon and their ancestors anyways.