I would've thought of this issue as coming under this rule:
4.12 Kill boxes - Kill boxes that expose a part of a players hit box through the collision box of a prop are not allowed
This is a rule for building bases, but I think it was intended as a rule to stop people from doing what Tyler did in the video. At this current time, I believe what he did was not against the rules, but it definitely should be a rule or it should be made clearer in the rules that abusing the hit boxes is not allowed.