I do not have an icebox, but those that do might be able to confirm/deny this. There is a small hole below the filter to allow any water that gets sucked up to drip out. And if you hit a puddle, or a small lake rather, that completely submerges the inlet to an icebox you would really need to run your car at WOT to suck that much water up and then saturate the filter so that the water gets to the engine. And even at that the filter would have to be pretty much submerged to hydrolock the car.

If you are sitting in a large as puddle with your car at WOT then you pretty much deserve to have your engine hydrolock. Not saying you would do this but it would have to be a damn freak accident for this to happen. All the planets would have to be in alignment while hell is freezing over.