John Locke, Montesquieu, Aristotle, Hobbes, Plato, and Rousseau never set foot in the US either, but ALL of them greatly influenced the writing of the constitution. And yes, de Vattel was one of the MOST influential. The capitalized Law of Nations mentioned in Article I refers to his work.
And not a thing one of them said is the Supreme Law of the Land which is reserved to the Constitution, the Laws made by Congress and the Treaties ratified by Congress and signed by the POTUS.