As to the military aircraft near you but not within the 5nm. If you are flying in controlled airspace, military aircraft will route around that airspace whilst operating in the open FIR or their restricted airspace.
As far as military aircraft not squawking. In the 16 years that I was in the game, we would have a Mode 3A and C return (plus a bunch of others that you can't see). The squawk would either be assigned by ATC, Fighter Control or be a standard conspicuity code. In the UK we always used to have those nice VFR slots through airways but still normally took a RIS. Even when we were transiting the open FIR we would normally make use of a RIS until we got to our play area.
My guess would be that ATC are feeding you a line coz guess what even if the yanks were flying their new super-invisibility hyper-sonic space spy speeder plane through your airspace they would have a radar reflector attached so that all players could see a primary return. Think about it from their point of view, they don't want you to know what they know about what you want to know about what you would really see on the radar as it flies by.
Ghost