I would be more worried about electrics I think personally. If I'm going to go through that much water for that length of time that the RAI can't handle it, I'd be more worried about the electric gear going fowl.
The wading depth I think is 700mm, that's pretty deep anyway, and if I thought it was going to be a bit deeper, I'd wrap up the front with a tarp anyway. The hose for the intake is not "water proof" as such, but would be water resistant.
I was watching the Land Rover Experience expedition (??) the other day with the Disco Sports. They drowned one, pulled the air filter out and replaced it, and away they went. Obviously the motor was either stopped by the operator or the electric system saw the fault and shut down. Either way, they didn't hydrolic the car.

