Not a Cincinnati guy, but I have eaten chili there and made my own, and I’m gonna second that

But I do add some cocoa powder to my regular chili recipe, and people rave about it. Sounds a bit weird, but consider, for a momento the existence of Mexican Mole sauces that often contain chocolate. I’m not adding much, it doesn’t taste chocolatey, but it does add something nice to the whole flavor profile.

Adding it to Cincinnati style chili wouldn’t be traditional, but I could definitely see it working very well with the flavor profile if you didn’t care about making it authentic