Do fighter jets have a traditional inverted fuel system?
I don't know for certain as I'm not military, but I imagine that they pressurize the fuel tanks using bleed air, much like jet airliners do. It's also likely that they make use of boost and ejector pumps to provide positive pressure directly to more centrally-located tanks which the engines then feed from.


(from FAA AMT Handbook [pdf])

The F-15 has both wing &amp; fuselage tanks; according to a site of dubious accuracy (F-15E.info):


  The left and right engine feed tanks contain baffles in order to provide a limited amount of fuel to the boost pumps during inverted flight or during negative G maneuvers





  
  Left wing tank
  Auxiliary tank
  Left engine feed tank
  Right wing tank
  Right engine feed tank
  Tank 1 (main tank)
  


Baffles are dividers in the tank itself that limit the speed at which fuel can flow from one end to another, usually to prevent fuel sloshing and screwing up balance.