Cool website and crazy video. What was with the tarp on the white land cruiser? Can see it helping until they hit the other side and lost all momentum.
The tarp provides an air pocket for snorkeless rigs to help prevent water from getting in the intake. If you keep you speed right, a bow wave forms and creates an air pocket in the engine compartment.
Most of these guys/gals are nuts in my book. Hydraulics is nothing to mess with and even with a snorkel, some of the currents shown could have easily turned a fun adventure into a deadly disaster.