Chorus doesn't necessarily do any de-tuning. Generally, it will apply shift to a copy of the original audio. So it should just be the same audio, except a little delayed. Chorus plugins can have tuning capabilities, but then we're talking about tuning, and not chorus.
Adding harmonics is an entirely different thing and is usually associated with EQ. To simplify it, harmonics adds pleasing distortion.
If you mean plugins that adds harmonies, then these are typically a mix of chorus, and de-tuning, but that's also oversimplifying. Plugins designed to add harmonies also have more going on under the hood so that the effect isn't as robotic as just adding chorus and tuning, and yet it still sounds very robotic most of the time.
