I can tell you what he's doing my friend...or moreso, what they're doing.
Sounds like there are two guitars in the mix here, we'll call them A, and B.
Guitar A sounds like it is playing an octave power chord, which is like a typical power chord except you remove the "fifth" so that only the low & high octave (same note) of the chord are playing. In this case, the tone suggests it's an octave power chord played somewhere on the low end of the guitar (ex. Somewhere on E, between frets 1 and 4). To add, they're playing this chord extremely fast. There is also chance it is simply a guitarist plucking a single low end note coated with lots of distortion.
Guitar B is playing an octave power chord as well, but at a higher pitch, essentially adding a bit harmony to the whole sequence/progression. This player is also strumming at a very fast tempo and more than likely has added a bit or reverb (perhaps leslie pedal/FX) and a bit of chorus/delay to widen up that sound.
If your DAW can simulate Q-Flam with MIDI (ex. Logic) look into that, as it can somewhat replicate the strum of a guitar. You would want to program it to be dominantly "down" strums.
If you were to do this in a synth environment, you'd want two synths (one for the high part one for the low part). Perhaps a very short attack/release time, probably 2 OSC (saw + sqr) and then really just flavoring it with your choice of filters, distortion, etc. Perhaps mod the filter with a key tracker so that it opens up more the higher the note that is played (like a wah pedal).
IMO, to really get that true guitar octave strum sound, you need to record it from an actual guitar. VSTi's have certainly come a long way...but there are certain sounds that are best suited to be performed by the real instrument.
Cheers.
