Think about it. Air is a lot easier to move than water, agree? So, why would the suction of an intake ever suck up water when there is air to be sucked up. Like Daniel said, unless you put your intake into a situation where the only option is to suck up water (immersion of the filter, or in ice box the down tube) why would it ever do so? IF you want do demonstrate this, take a piece of tubing of some sort and pull air through it with your mouth. Then do the same pulling water through. You will find that the air was easier to pull through. Finally, submerge the tubing's opening partially, leaving space for air to get through as well. Now suck and see if you pull up water. I think you will fing that not enough will be sucked up to "hydrolock" your mouth. Not to mention, unless a road is completely flooded, driving through a puddle is a relatively short experience, leaving less opportunity to suck up water.
THe chances of encountering hydrolock are fairly low with an icebox because total submersion is easily foreseeable. If you need to cross a flooded road, pull over and use your handy-dandy screwdriver to make a temporary short ram. Problem solved!
