I think such a rule should be added, but with different phrasing, as metagaming is different from what teaming in TTT is.
1.8 Ghosting/Metagaming
Using Admin Chat, Psay (!p name message), or speaking through third-party software outside of the game to give players an unfair advantage or access to information they should not know. Should you be talking to other players inside of your game through a third-party software, admin chat, or Psay((!p name message) you must not disclose any in-game information. [i.e who you died by, who the traitors are, to revive you, calling out your T buddies etc.]
What I believe should be under teaming is:
-Cooperating with other players to purposely disrupt the concept of TTT.
Example: what jam said the comment above.
The context behind this is a bunch of people put on the trump skin and claimed an area called "trump Island", the traiters in the group would shoot anyone that came close and the innocents in the group did not kill the traiters for kosing of of location, hence the teaming part, he is basically saying the innos who didn't kill t baiters should be punished.
in my opinion this would be hard to implement as you can't do much without video evidence plus as long as the innos don't start shooting it's just having fun and it's rare that this kind of thing even happens, it's not such a big deal we should make a rule about it
-Teaming with other players to RDM/Helping players from the opposite teams.
Example #1: Two players sitting on top of tower, one being a T, the other being an innocent, and they don't kill each other but both shoot other players.
Example #2: A traitor revives an innocent and they don't kill each other.
Example #3: Player A (Traitor) kills other innocents, doesn't id bodies, and player B (Innocent/Detective) kills anyone that shoots him.
Of course, following the examples above not everything should be considered teaming, because sometimes Traitors kill other Traitors due to circumstances, and then if an innocent protects him it's understandable. Hope I'm making my point clear.
I do think, however, that without Death Scenes being fixed this is a bit harder to prove using just the logs. Not impossible though.