No. The all-weather IP66 rating of the fixture ensures that the inner parts in the lamphead are completely free from dust, dirt, or water ingress. However, you may want to clean the external housing and heat sink of the fixture with a hose, just to make it look better to the eye.
SkyPanel X is an IP66-rated fixture, and therefore is protected against powerful water jets (100 liters per minute at 3 m distance with a 12.5 mm nozzle from all directions). This must be clear cold water to avoid corrosion and other material degradation, and never related to high-pressure jet or steam cleaning, which corresponds to a different rating.
When you are performing the cleaning, make sure your fixture is off for maximum safety, with the caps in the connectors always on (except for the LEMO connector, which doesn't need it), and avoiding water jets directly over screws, gaskets, connectors and the climate membrane. Even when the fixture can withstand the test when coming out of the factory, we cannot ensure the fixture will continue to be IP66 if serviced and not properly re-sealed. Contact your ARRI Service Team for more information on how to do this properly.
ARRI did not only test SkyPanel X in its facilities and on the field, but also via a serious independent lab: TÜV Süd. The test includes a dust-tight test (IP6x), a waterproof test (IPx6), an electrical safety check after both tests, plus an overall overview on searching for any trace of water inside of the fixture after all testing is performed.