Okay, first off there are different degrees of sociality, these can range from animals that are solitary do not interact outside of territorial defense, resource defense and/or the breeding season, to animals that live in permanent mutually interactive groups to animals that can live in large groups that may or may not be related (E.O. Wilson does a good job of covering all of the variations in one of his books, I'll post the info on the book later today).
While some very social animals engage in cooperative hunting (dolphins, cetaceans, various canids, wolves, chimps, some ant species to name a few), spontaneous cooperative hunting is also seen in animals that are not very social when the conditions are right, some sharks, mata matas, (I have seen it in walking catfish), to name a couple off the top of my head.
The fact that axolotls can interact (otherwise they would not breed) does not mean that they are social in the sense that wolves, dolphins or primates are social. The observations listed above by some observers pointing out how the axolotls "hang" out together also does not mean that they are social in the same manner as a primate but that there may be resource guarding (such as mate or potential mate), niche preference (the microenviroment at that spot is the best in the enclosure) or other reason.
I would have to say that in the classical sense axolotls are not social.
Ed