Brushed Motors are even SAFER under water than Brushless!! Some Old Farts even break their Brushes in by running the Motor IN a glass of water!
One IMPORTANT distinction with Brushless....
Nearly ALL RC Aircraft Motors are Sensorless.
SENSORED Brushless Motors are an entirely different story. If they even get more than damp, their internal circuitry will FAIL.
There's even exceptions to that - RC Crawlers often use Sensored Brushless Motors that have been MADE Waterproof....
They often start at about $90-100, and can go as high as $300!!
.... If all you have coming out of your Motor is THREE Wires - then you have a Sensorless Motor.
If you have Three Wires AND a Harness Plug, it's Sensored Brushless, and CAN'T get wet!
Hope this helps. 😉