No it is not.
When I first got my van, I gave it the 5 gallon bucket workout and was satisfied that whatever caused other filters to get wet wouldn't affect mine...but 3 months and plenty of rain/snow later I've been proven wrong.
Yesterday I pulled the cover to eyeball it and indeed, the small "pre-filter" thing was damp. There was a little bit of water down in it's hole. The big part of the filter was dry.
We've had a LOT of rain here in Denver recently, and I specifically chose to inspect it after it had stopped. Water does get past the gutter, funnels, etc... and in the past I noticed a bit of it sitting on the place where the two pieces connect.
Somewhere in the rear left corner of the box is where the water is getting in. It's a very small amount. I'm going to modify a mini TURD for it.