Here is my theory on the whole thing. Unless you have an agreement to the contrairy you should always err on the side of being too ethical. If you have to ask, DON'T do it.
On the other hand, if the league has an ongoing practice or an agreement then that overrides the above statement.
2 examples of this are 1 my biggest $ league has an anything goes policy. You have control over your own roster and trades and can do what you want. 3 years ago we had two players trade their draft picks making one better in one year and the other better in the next. Year 1 the team with the extra picks had a couple of injuries and noone would trade with them. The eventually fell out of the playoffs. The second year when it became clear that the team that had the extra draft picks that round was the favourite to win the teams that were out of it all worked to help his opponent win the game. The opponent screwed them all and didn't give them their players back in the off season and ended up winning last year as well (keeper league) basically this league is self-policing. Knowing it in advance you plan for it.
The other is actually my favorite league. Each team is expected to be competitive no matter what but the commish is not going to get involved in anything but the most blatant cheating. Anyone who acts unethically will not be invited back the following year. Knowing that the commissioner was not going to get involved, I had no issue when he refused to make a line-up change for me even though I sent the email before the deadline because the site was down and I couldn't log in to replace an injured player. I was playing his wife and I ended up losing by 2 points. If the policy wasn't clear I would be concerned about a conflict of interest for the commish but knowing that he has consistently not messed with rosters for any reason I didn't feel slighted.
I hope the teams didn't bench their line-ups unless it is a rule in your league to do anything to win.