Sure we can.
Just like we can know it's not a pine tree.
Words have meaning, you know.
What you're doing is emptying your word of meaning, then making the obvious claim that it's now not inconsistent with anything you care to dream up.
All I-don't-know gods are Humpty-Dumpty gods by definition.
That's because the idea of god, like the idea of anything else that's not nothing, originated with a notion of something.
In the ancient worldview, gods had a place. They had qualities and actions.
So the I-don't-know gods -- whether you're talking about "the unknowable" or a deistic god or an ineffable god or a hyperdimensional god -- cannot be anything besides a radical re-definition of the term to mean something it could not have meant.
It's like I said before, you can't simply declare that, actually, phlogiston didn't have any of the qualities everyone said it did, but in fact it's something we simply can't know, and by that maneuver salvage the claim that phlogiston is real.
It's the same for anything else, including gods.
A Humpty-Dumpy god is no god at all. It's like me saying I've got a pet bird, as long as you don't mind that it's got no feathers, beak, wings, feet, or body.
I-don't-know gods are mere Humpty-Dumptyisms, by definition, and so have nothing to do with an actual discussion about whether gods are real or not.