VG won't actually "clog" atomizers unless it isn't thinned with water or an ethanol and water mix. Even then, it isn't really "clogging" the atomizer. Glycerol has a high boiling (read vaporization) point, but this is reduced (drastically) by the addition of water. Thus, if someone is trying to vape near-pure glycerol, not only is it going to be too thick to "flow" it is going to cause a problem as the atomizer will have to get a lot hotter than it was designed for.
Also, it should be noted that glycerol leaves absolutely no residue when heated and vaporized and is not, chemically speaking, able to "gunk up" an atomizer.