I really don't think it's cheating. I suppose it depends on the trade and the league.
Perhaps it's because the only situation in which I can see this happening is in contract leagues with kickers and defenses... I have one kicker, you have two kickers, my kicker is on bye, neither of your kickers are, I trade you my kicker for one of yours, plus maybe a future draft pick as compensation.
My feeling is that if the trade itself wouldn't be considered collusion (i.e. it's not LT for Taco Wallace or whatever), the reverse trade isn't either. Obviously if the trading itself is collusion (trying to stack a team, whatever) then it's bad.