I've gotten tired of seeing this type of nonsense on UB, so I've forwarded a stream of complaints to them. You can do this within the UB client by clicking on customer support. I hope you complained about the example you mention.
It's not just a matter of opinion that it is wrong to agree to check it down when someone is all-in. This is explicitly covered
in UB's rules. It is clearly worse to agree to attack another player.
At the table, people will argue with all sorts of nonsense, but I think UB does take it seriously. Please post here if a tournament result is changed, or ought to be changed and was not. So far, I haven't seen any direct action, but UB claims that it has done some things.