If you know the other player is hacking and you team with them you should be punished
The problem with that is, there is no clear way that someone could report that. The friend could just say he didn't know that the guy was hacking, also there would be a LOT of controversial bans being dealt out if this got implemented. Boosting seems like what you are describing here, which is getting a team and having them /kill at deathmatch repeatedly to "boost" the amount of wins that the player has. If that is the case, you would need a lot of evidence to support that, including video evidence, leaderboard statistics, and trying to find the times that player's died repeatedly. Teaming with a hacker isn't against the rules, because there is no way to prove that the person teaming with the hacker even knew that the person had hacks.
Let's say a new player joins the server. He asks someone to team with him so
LeafyGreenTea says he would team. The new player sees leafy go and kill everyone at once and thinks "wow leafy is really really good!". Now, is it the new player's fault that he teamed with a hacker? Even if the hacks were obvious, how can you prove that the person knew? Some people may not be able to tell what are hacks. We shouldn't punish them for that.
Another example would be if an experienced player teamed with a hacker. Now, if someone reported the hacker and the legit teammate got banned as well, he would be easily be able to dispute it. He could just say he didn't know the guy was hacking. There is nothing that the staff can do to read their minds to decide whether he is telling the truth or not. He could be completely lying but there is no proof that someone can grab that will prove that they knew the person was a hacker. And honestly, if the hacker gets banned, that kind of solves the problem in itself. The teammate will no longer have an unfair advantage by teaming with a hacker.
I personally teamed with a hacker before. Granted I had no idea he was hacking until later, because I never saw him pvp someone. And when I did, I saw nothing that suggested hacks, there was no head flipping or anything of the like at my angle of view. The only reason I figured out he was hacking was when I was spectating and I saw him fight someone and he completely wrecked them. It was obvious hacks there. Now, should I be banned for that? Of course when we fought in deathmatch he turned his hacks off, so I had no idea he was hacking at the time.
So long story short, merely teaming with a hacker probably will never be ban able due to the fact of all the conspiracy and guesswork that would go into it. The hacker should get banned, but the legit player should remain fine. Now boosting is a whole different story. But that requires quite a bit of evidence to prove.