[GuidoK]

The supercharger itself is pretty resistant against the pressure washer.
But don't aim it directly in the pulley.
In there is a hole in the centre of the pulley that is I think a spill hole for the oil.
That's the only thing I can think of when (mildly) pressure wash the twinscrew. (apart from your open air filter)

The most vulnerable parts are the sound dampening, connectors (mostly the area where wires come out), and tape/cloth wound around the wires.
I also use compressed air to dry the parts/ blow the water away. But that also can damage the sound dampening etc. but you can get water out of parts that are otherwise unreacheable.

When using a pressure washer always keep the nozzle 1m or so away from the engine.