I have never seen domesticated dogs throw up from face licking… it is grooming and bonding with domesticated dogs. It may well be hold over instinct in some way, but having had dogs, litters with moms, if licking caused puking, I am sure I'd have seen it.
But I went looking, and while I couldn't find it on NGeo site I found the following. But he is full of it. Even in the wild, dogs lick to GROOM, bond, etc also:
http://www.4vetclinics.com/articles/dog-licks-face.php
In the wild, there’s only one reason why dogs lick, and that is because they want more food. Take the wolf for example; when a mother returns from the wild after searching for food, she will be greeted by constant licking from her young. This is because a lot of canine animals in the wild have a regurgitation reflex that is triggered when their face is licked. This means that the young know that they will have access to food when they lick their mother, as they will just be feeding on her vomit. While this may seem quite sneaky on their part, the mother also knows this and decides to go along as it’s easier for her to carry the food in her stomach.
Well, before we continue, it’s worth mentioning that the vast majority of pet dogs don’t have this regurgitation reflex so won’t be constantly vomiting!
BUT found this one on wild dogs
http://www.umich.edu/~esupdate/library/97.01-02/mamakos.html
Once numbering in the hundreds of thousands, the African wild dog (Lycaon pictus) is now one of the African continent's most endangered animals. It is believed that fewer than 5,000 wild dogs currently exist in the wild, and their range has declined from 33 to 15 countries. The largest populations exist in Botswana, Zimbabwe and Tanzania. The initial population reduction came during the early part of the century as a result of a very successful extermination campaign led by ranchers who feared the loss of livestock. Today, the effects of diseases (e.g., rabies, canine distemper, and parvovirus) spread by domestic dogs are having an even more devastating effect on wild dog numbers. Of additional concern is inbreeding due to the formation of genetically distinct groups of dogs in the southern and eastern regions of their current range.
Wild dogs are about the size of a German shepherd, have long legs, large ears and mottled fur of browns, black and white. They live in tightly bonded social groups or packs of 2 to 30 individuals led by a dominant male and female. Pack members exhibit well-defined greeting behaviors, the most obvious being affectionate face licking.