And is an [non-disclosure] agreement binding upon a conspiracy to commit murder? Howe about felonies? Guess what: this spying is a felony-class law violation, in more ways than one.
So then — is Snowden bound by his NDA?
Maybe not morally or ethically, but he is in the legal sense. Just because a law is bad or being perverted does not keep one from being convicted/punished under it.
Kind of like the arguments about whether a psychiatrist or priest is bound by the confidentiality precepts or if they need to "rat out" someone who has murdered or may murder. There will always be conflict and doing the right thing also results in at least some modicum of the wrong thing being done.