Why would not being a theologian make a philosopher a skeptic? They could be religious without being a theologian.. A philosopher who questions the existence of God could be considered skeptical in a narrow sense, but that would not classify them as a skeptic in the general sense.
Hume was a skeptic not because he questioned the existence of God, but because, although he was an empiricist, he questioned the validity of knowledge obtained by induction.
I would not consider the others as skeptics.
Nietzsche’s morality differs from traditional religious morality, but that does not make him a skeptic.
Aristotle was not a skeptic, in either the narrow or general sense. Aristotle thought of God as the Unmoved Mover, who was necessary to keep the world in motion. Early Christian theologians had no trouble adapting Aristotle’s philosophy to Christianity.
I did a search for Kant and skepticism and found this quote. Would that make Kant an anti-skeptic? Kant believed in God. He said that you cannot prove the existence of God by reason but through how we experience the world.