Brushless should not be run under water. They are water resistant but if you fully submerge them for to long water will get in them and sling everywhere and cause a mess if you know what i mean.

The new E Revo has a MMM system and is not waterproof. It comes with a 2.4 radio though which should be somewhat decent for beginners.

The VXL esc is pretty waterproof. It has tons of O Rings in it so its pretty sealed, my friend has driven his through many puddles. I was out driving my pede with the vxl motor and sidewinder esc in the snow and it seemed to do fine. I heard the sidewinder is pretty waterproof also, and as for the MM you just seal off the USB post and it should be fine. As long as you have a gear cover on so no water gets on that end of the motor then you should be fine running the vxl in wet conditions. However if you submerge any electronics you better be expecting to buy some new gear.