What I realized is that when playing with a controller ADS (aim down sight) is practical, but when using keyboard and mouse then a counter-strike style of play is better suited. Discuss
I'm not sure what is used here. Although it is VorpX, which is kinda of a hack in the first place. But it looks monoscopic, custom-rendered, with no variation between the right and left eye.
The gun is clearly stereoscopic when not aimed and just carried around, but not so clear when aimed. In either case, the guy doesn't seem to bothered by that.
I don't really know for sure, but it'd be interesting to see the actual difference (i.e. one mode is pure 1-to-1 3D rendering of the gun model, the other is a custom weapon render meant to 'simulate' iron sights like in 2D FPS games).