Well, seeing that they're outside, they should be catching a bunch of insects on their own. I would say that Cheetos wouldn't safe to be on the safe side...But if you REALLY think that they aren't catching enough insects,(which doesn't really matter since they can live without eating, as long as they get plenty of light and water) then try experiementing with just one pitcher, see if it rots or not. I would think that the Cheeto would clog up the pitcher anyway, meaning ants wouldn't get to the bottom and be digested.
So, if I were you, I woulnd't try it. I would just collect ants and other bugs. I guess using Cheetos to collect them is fine, but actually putting them in the pitchers probably isn't.