Oliver runs hi-hats through the FLVTTER plugin, using sidechain distortion to lock the high end to the low end for a more glued drum sound.
Setting the plugin's sidechain input to a kick makes it distort the hi-hats in time with the low end. It adds grit and character while also ducking the volume slightly, like a sidechain compressor.
Pushed to the extreme, it starts to resemble the crunch of slamming a mix into FL Studio's master clipper. Used subtly, it just tightens things up without calling attention to itself.
The technique isn't limited to hi-hats. Any high-end material, noise layers, vocals, cymbals, can get the same treatment to feel more locked into the groove.