The fog certainly frustrated the external observers, but it doesn't seem ideal from SpaceX perspective either.
All the external observers were very distant from the launch/landing site and would be ground-based. That would make it very difficult to see through even a very light low-lying fog. So certainly all the external observers had a hard time with the fog.
However, it also seems less than ideal for SpaceX. They obviously have a lot of on-board instrumentation including numerous cameras and they presumably have several redundant telemetry links (though not very reliable in this case). So they must collect a huge amount of data by this means. But I assume observations from outside the craft are also very imporant in confirming altitude, velocity, attitude, exhaust-composition, structural integrity, etc. Perhaps visibilty from closer-in cameras and from cameras positioned higher up or on drones was considered good enough. Or maybe there was an FAA launch window that was about to expire?
But my question is: why didn't the foggy conditions seem to pose any problem to SpaceX. Why not wait a few hours for the fog to clear?