Not a Quest (I've used both and think it's the same answer), but with the HTC Vive the foam pads do a good job of not letting sweat get to your eyes.

In general, the facemasks are pretty tight around the eyes, and the sweat glands are on the forehead, so it doesn't affect operation.

Of course, it still gets gunky and you'll want to regularly clean the facemasks if you do any exercising in VR.

The Quest specifically has the face mask directly integrated to the spacer, so you have to remove the whole thing to clean it, but it's doable.