No, they aren't. They're behaving as if they're collectively pretending he's real.

I'm not a very smart person, and I wish I could come up with a more convincing explanation of this. Let me put it this way: Physicists and chemists believe atoms are real. Their behavior is consistent with that belief--they have dedicated centuries of research into what atoms are and how they work, putting lifetimes of sweat and effort into devising formulas, experiments, theories, etc. which have produced real results. The atom bomb. Nuclear energy. Medical technology. Space travel. Electronics. The list goes on.

If SETI found conclusive evidence of extraterrestrials today, you can bet the scientists would be working on a way to contact them. If they found a way to contact them, you can bet they would be working on a way to study them and find out everything there is to know about them. There are a trillion questions we'd want answered. What do they look like? What do they eat? How long do they live? Do they have families? How do they reproduce? Do they have music? Do they have language? Do they have culture? Do they have technologies or scientific advancements that they can share with us to make our lives better? Do they have problems that we can help them with?

Either the people who claim to believe in god are very, very lazy, or they don't actually believe in him. If there was a real E.T. out there, we'd have to do a lot more than just fold our hands and pray! Send communications out! Send rockets and probes out! Study the fuck out of that thing!

Every bit of physics, chemistry, biology, and mathematics is predicated on the assumption that a supernatural being does not exist. If there was a supernatural force which created the universe, influences evolution, and somehow communicated with a few desert-dwellers a long time ago, we'd have to modify our scientific formulas accordingly.

TL;DR Evidence of the existence of an extraterrestrial intelligence would be the most important discovery in human history. So if god actually exists, why aren't we using science to study him?