@gaigous.
Not exactly.
The real deciding factors are d*mbness and the amount of bad luck / the missing of good luck.
Even if person if fugly they would survive if they are clever or/and lucky enough to avoid getting bitten.
For example the black haired fugly one was simply too d*mb to notice the danger of insulting a person who had already been bitten and holds onto her.
Anyone with a working brain would have pretended to get along with the bitten person first to then get some physical distance to her before they would cut ties with her.
That way you would prevent her from suddenly biting you.
It is just that authors probably want to save the effort of creating a beautiful face to then not use it again.
Using a fugly appearance for soon to die characters saves them time as well as the effort from having to watch out not to make future important characters look similar to them which also saves a lot of time and effort in the long run.