The South Park episode actually had help from Blizzard to get the models to do things they normally wouldn't be able to do in-game. If i remember right the episode was originally going to be in the regular South Park style until Blizzard found out about it or the studio contacted them about it.

It really shouldn't be against the TOS since you're essentially recording a roleplay (albeit a scripted one), and roleplaying or gameplay videos aren't against the TOS. As long as you credit the game and don't hack it to do it there really shouldn't be an issue.