Journalists and aid workers in a war zone are about as far as you can get from a bunch of federal employees working for the CIA at the pentagon. Those people that ISIS has beheaded on video weren't picked because of what they were doing, they were just easy to find, capture, and killing them gets a rise out of the civilized world.
If anyone at the pentagon thinks they work there secretly they are fools. All you'd have to do to determine who works there is set up a series of hidden cameras to capture plate numbers of vehicles entering the facility. Then feed those numbers through a batch of people who have access to the national plate registry system, cops do this for practically every traffic stop. It would be a joke for a nation state to obtain that kind of information and it is definitely inside the realm of possibility for groups like ISIS or AQ. Some of the vehicles will be essentially government limo service, which makes tracking the identity of the person being given such privilege a little more difficult but it also tells you a lot about their value as a target.
The Oklahoma thing was only tangentially related to ISIS. It was a work place violence issue and the method he chose on the spur of the moment aligned with his sympathies. This is really only an issue at the Pentagon so far as regular work place violence is.
Operational Security is a real thing but it doesn't really come into play when talking about an eating establishment labeling you with a name inside a secured facility.