The Chorus parameter adds modulation to some of the reverb internal delays.
This kind of modulation was inherent of the first reverb algorithms (EMT 250, Lexicon 224,…) to avoid metallic ringing on the reverb tail.
Like other parameters, it applies on all the reverb algorithms. You can try to change from Off to Strong with a long reverb decay time to listen the action of this parameter.
The Chorus type is a 8-voices chorus along with a reverb. So you can also add the chorus parameter to the chorus type ! I agree that it can be confusing.