What methods are used to perform head tracking in the cockpit?
Accelerometers are used, however for lower latency and higher definition, tracking infrared emitters is the better choice1.

The A-10 as you wrote uses inertial or magnetic trackers. The Eurofighter helmet uses infrared tracking.




  ... the Typhoon’s HMSS features lower latency, higher definition, improved symbology and night vision.


It's the one on the left (1source).

You can already see it has an organic brain of its own; those bumps are the IR LEDs for tracking.