Classic capture. Would the government's decisions be biased by knowing that the financial decisions it makes will directly affect its old (and future) colleagues? The bureaucracy can buy product A from a random company, or product B from their old boss's company. And also have some assurance that in the future, the second company would offer them a job. All the while, product A is the better product.

This is not nearly to the level of 'constitutional protections' - but is instead another indication of the inability to properly regulate an entirely secret bureaucracy. The NSA has all the failings and issues that any other large bureaucracy has - however it has difficulty utilizing the common mechanisms to regulate its less efficient behaviors.

Government workers going to work for defense contractors is not new.