Took a split once, years ago. It was a 32-team league, and my best player at the time (Adrian Peterson) was doubtful to play in the final week. Seemed like a no-brainer to me, since there was about an 80/20 chance I was losing that matchup. But, for whatever reason, the league (or at least some of them) had a huge problem with it. insinuated collusion, which was laughable. Basically asked us to leave at season's end, which after the drama, was fine with me. I didn't know the guy that I split with, and clearly the others didn't understand how "collusion" works.
Here's the caveat to the splitting thing.... If the two teams involved have been making trades throughout the season, it becomes a questionable (or borderline bad) look, in my opinion. That wasn't what happened in my case. Neither of us had made any trades all season, much less with each other. But, in the instance where two teams trade in-season, and then split the pot at the end, it begs the question whether it was planned all along.
Now, granted, I get it... It's a plan that is a longshot of actually panning out. But, it is what it is... If two teams are "working together" by trading with each other (or maybe ONLY with each other), with the agreement that they split whatever winnings they end up with, it potentially gives those teams an unethical advantage in some situations.
Bottom line... I've done it once, never before and probably never again. And, generally speaking, I don't see a problem with it. What two teams decide to do during championship week is their business and their business only. That said, if there is any hint at all that they've been working together in-season or made the agreement to split prior to that point (either of which point toward collusion), that's a pretty bad look and I totally understand why people would have a problem with it.