Server to client syncing in the BLAM! engine is a complex task so the fact that the lifts work at all on the client side is a fucking miracle. They do have some kinks (lag mainly) but they work pretty well. The effect is created by continuous damage_effects that are created to fling the player straight up into the lift chute and into the map. A simple sound file is added to the damage for the impulse sound a invisible marker with a sound_looping tag plays the looping plasma noise.
The plasma pit that makes up the gravity lift is just a stacked shader to make it look 3d.