The Uvi rely more on water to breathe, not necessarily to stay moist. Their skin is very touch and easily sustained outside of the ocean, their lung and gill system is not. The wind gusts could easily move them, but it won't damage their skin or ability to survive very much.

While the Uvi won't be able to utilize the fog with their own magic abilities, it also isn't much of a deterrent. Because Aimintas is a world with a lot of water, fog isn't an unnatural phenomena and something they would be familiar with. The Uvi have pretty decent eyesight, so a fog would inconvenience them at the same level as you would be driving through it -- it's kind of a hassle, but you can still get from Point A to Point B if you're familiar with the area, which they are.