Pretty often. When I was at a defense contractor it was the standard term for when you didn't want to say soldier/sailor/airman/marine/etc.

https://trends.google.com/trends/explore?q=warfighter&date=a... has videogame-related spikes, but doesn't show any recent increase.

Thanks for replying - so its used as a generic catch-all term internally? Did previous DoD secretaries use it in speeches? I thought they used bureaucratic terms like service member. I guess that doesn't work in casual conversation...