The OP seems to be implying the possibility that Snowden purportedly took the Booz Allen job with the explicit purpose that of exposing what he perceived as NSA's unethical practices. Now, replace "Snowden" with...well, a hypothetical whistleblower, and "Booz Allen" and "NSA" with [company/institution you respect]
e.g. Henry Ford joined Tesla Motors to get the access to documents that prove that Elon Musk is cutting corners just as Ford suspected.
There have been unfair and trivial criticisms of Snowden, but this particular angle is not completely trivial. Note, however, that even if true, it does not dismiss Snowden's claims or findings...but it's the kind of pre-condition that must be weighed as it would be in any controversy.