I thought their oath was:
I, [name], do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter. So help me God.
5 U.S.C. §3331
I don’t see anything about obedience to the DHS there.
“Meine Ehre Heisst Treue”