We would say that the divine essence cannot be seen, and is outside our ability to know. God is witnessed through the things that are created. We see God through a veil, only by the divine energy that is everywhere present and fills all things. We of course would say that God knows all things, even better than a human could, because God is always present. The omniscience of God is something completely other and beyond what human knowledge can comprehend. It is beyond knowing. Divinity and creation are united in hypostasis, and this hypostasis is God enfleshed with creation, clothed in majesty.
In this hypostasis, the divine and the created are united together, without confusion or separation. Divinity and creation both have distinct physis or natures, so they are not the same. The hypostasis is not half divine half creation, and the natures are not confused. The hypostasis itself is fully God, and all of creation is united to it in divinity.
To say that God does not interact with creation could not be the case. It is God that both gives everything in creation its existence, and is there giving everything its action. When we do something, it is in and by God that we move.
Everything that is known is creation. So yes, there is a common nature of known things.
God if we were to compare God's existence with the existence of any created thing, we could even say that God is beyond existence. Even the term, "Ultimate Reality" does not capture how distinct the nature is of this existence when compared to other examples of existence. We are talking about the source of all existence, the sustainer of all existence, and that which even the things that have passed and have yet to be find their existence.