They may not believe in the Abrahamic God, but they do seem to believe in something. What exactly that is can be debatable. But they have worship services, they have rituals, they even have concepts of the afterlife... can they really be classified as "atheists" at this point?
Unless, of course, they're willing to admit that the whole thing is a joke... but then they would lose their attempt to be recognized as a legitimate church in Germany. That's really not much of a foundation to build a spiritual life on.
It may be an amusing idea, but seems more like some sort of fraternity prank rather than an attempt to find the Truth. Those who are seeking God and are more spiritually minded will quickly figure out that this isn't the place for what they seek.