Vattel was the legal foundation for the constitution where it was needed. Therefore, your question is stupid. It is not I who attempts to disparage the constitution as written, neither do I seek to weaken its boundaries and restrictions on human greed.
Just about everything that had been written on law, politics, and etc, contributed to the legal foundation for the Constitution - the Founders were pretty well, and widely, read.
And no, my question is not stupid, it is designed to clarify the discussion by clearing away the haziness and muddy thinking that can come from focusing too much on one’s favored interpretive aids and not enough on the text being interpreted.
The simple answer is this: no, Vattel is not in the Constitution. There is no part of the Constitution that cross-references or otherwise expressly and explicitly incorporates Vattel into the Constitution. Therefore, Vattel’s value is at most persuasive, and as such, may not persuade some of us. Furthermore, even if one grants that Vattel is a source to be used as an aid in interpreting the Constitution, that does not commit one to adopting Vattel. The question still remains whether Vattel’s concepts were, in fact, incorporated into the Constitution, or if it is just a case of convergent evolution of the words used. Finally, there is the question of whether it makes any sense given the entire text and purpose of the Constitution, to incorporate Vattel’s concepts into the Constitution.
That this is how Constitutional interpretation goes shouldn’t be that much of a surprise. The Supreme Court itself engaged in an interesting exercise in the series of cases leading up to the Income Tax Cases that involved the various attempts to put meaning into the phrase “direct tax.” The phrase “direct tax” seems, at first glance, to be deceptively simple, but dig into first the text of the Constitution, then the contemporaneous discussions of, and relating to, the term, and finally the history and political context that the term existed in at the time of the writing of the Constitution, and all appearance of simplicity disappears.