In the story and art, there would be practically no difference in how it is portrayed and used. I accept the Snow logia as it can look and be used differently to ice.
I can see a fog paramecia, but not logia.
Hmmm talking about art. It could just look like the steam when luffy uses Gear Second and maybe Oda could limit the user so he can't grab people like Smoker does.
Ah what am I talking. It can be a filler DF or for someone who is already powerfull without DF. Like the fruit would only give him resistance to normal non-hakified attacks but since fog is less dens he couldn't prolly use it for offensive stuff.