I don't think it's "clearly collusion", but it is uneven. How long is your fantasy season? If it goes 14 weeks in the regular season, then it's still anyone's game mathematically. If only 13 weeks, it's still mathematically possible for the 2-6 team to get in, but more difficult.
Anyway, here's how I am thinking about it:
-Aaron Rodgers > Matthew Stafford
Obviously, but maybe not. Rodgers has been without Jennings and Nelson for the past 2 weeks and was pretty bad last week as a result. Don't forget that he had a couple lousy games early in the season thanks to that horrendous O-Line. I still think Rodgers is the better QB and capable of elite numbers, but Stafford finally had his break-out week last week and put up an insane total. So, both QBs may be trending in opposite directions. Rodgers is better, but not by a ton.
-Stevie Johnson = Brandon Lloyd
This is another case where it depends on what you're looking at. Neither guy is a #1 WR in fantasy, and both are actually getting a similar number of targets (Lloyd actually has slightly more). And while I'd rather have Johnson, they are almost dead even in total fantasy points on the year thus far (coincidentally both are on a BYE this week).
So yeah, it's a little lopsided, but to me, it's not terrible. If it were Aaron Rodgers and Steve Johnson for Matthew Stafford...then maybe I'd consider that collusion. But it also depends on if either of them happen to be fans of the players involved, or their experience with fantasy football. If either is a newb, or fan, that might be clouding their judgement, and I never step in the way of trades in those cases. It's not your role as commissioner to do that.
So, while I get your concern, there's still a lot of weeks left to be calling either team a playoff team at this point, and while the trade is a little lopsided, it's not terrible. Even though the two are friends, I'd let it stand.