They do not forbid meta-gaming through memories and known persons. There is no quid pro quo or agreement, it is just "I know I can work with Bob, and hey, let's do it again." Also, and here is something interesting, can you work with someone to make sure they finish near the top with you? Because, I believe from the allowance on metagaming, you technically could in the leagues.
Part of the league games is that there are certain people that are harder for you to work with. If you avoid those people, you kind of end up with the same set. Now, if you are always going to be allied with the same person, it could be a strength, but it can also be a weakness and taken advantage of. Honestly, I am not sure it is a problem. I am not sure I would want them anonymous.