First off, Adams was not an ordained minister. His father had encouraged him to be and his father-in-law was a minster, but Adams was not.
Adams was a minister in that was the title of an ambassador, when he served as a diplomat in France and England. But that was a political title, not a religious one.
As for the quote, "The divinity of Jesus is made a convenient cover for absurdity," please note he was not denying Jesus. He was saying Jesus was used as an excuse for absurd ideas. The full quote is:
"The divinity of Jesus is made a convenient cover for absurdity. Nowhere in the Gospels do we find a precept for Creeds, Confessions, Oaths, Doctrines, and whole carloads of other foolish trumpery that we find in Christianity."
In fairness, using the same standard I did on the Washington quote, I cannot find a source for it. Everything I found, starting with his entry in Wikiquote merely attribute it to him.