http://img74.imageshack.us/img74/3546/intake3dp9.jpg
That's the intake on my SC if you can see the front bumper and how low its hanging. I drove that thing through rain so bad the car couldn't maintain over 40mph even with the gas floored. It never even hiccuped (sp?). Yes hitting a big puddle at high speed can cause hydro lock with even a stock airbox, buts it very very rare. I've seen only one such case in the 3 years I've worked at a dealer. The puddle your car is in is huge, I would never have drove through that.
Yes it disturbs airflow, AEM even says it disturbs flow that's why they don't make it an option for the V2 intakes.
No it doesn't normally let air in, its controled by a diaphram.
I supposed it can be a good safety measure, but it was never nessesary on my SC for 3 years and some very intense weather.