Confusing edit.. anyhoo, the quests usually do spawn everything "somewhere", however that "somewhere" may be "behind the next hill, buried waist deep in the ground". And since That can happen, I wouldn't be surprised if "buried entirely under the surface of the next hill, on his merry way to bedrock" would also be a possible "somewhere".
But worry not, any wild version of the same zed will eventually count for the quest.