If one's serotonin is elevated such that their mood is elevated, they are in fact happy, no? So if DMT is elevated in someone's system, and they are having the experience of god, then that experience is real as an experience. Consider that it could be the experience of interacting with god that is more important than whether or not he "actually" exists. We can get blown away as it is just going to see a movie. If all it is is being in the most amazing, interactive movie with god, then I'm fine accepting that.
In the same way that TMS can be used on a particular region of the brain to regularly induce eidetic photographic memory of a scene from earlier in life, perhaps the DMT is activating an interactive memory of sorts of having interacted with god or something to that extent.