I'd be reluctant to risk it -- being able to see your drone is important, but more important, IMHO, is being able to see the airspace around where your drone is to make sure nothing else is in the same airspace. Even with the drone quite close if you take your eyes off it you can have trouble picking it back up again but usually that's not a problem so long as you know about where it is and that the airspace around it is clear. Though, technically, you need to have your eye on it at all times. That's kind of a problem given the need to at least periodically check your instruments (Go 4 app). Many of the rules are a 'best effort' but not quite adequate and therein lies the opportunity to not follow them.
Actually, the rules are pretty strict about cloud cover and how far away from and below any clouds you need to be. Fog is in most cases low clouds though the inversions we get in SLC area are also a mix of clouds and pollutants.
Brian