It is! Actually, it's possible for the entire OPN family. So, the Sega Genesis, the PC-98, and the Neo-Geo can all do it! Other FM chips can do a "one channel chord," but it uses sine waves instead and is far more limited Edit: I just remembered. The OPZ can also do something similar, but it works differently and is less practical overall
From what I can tell, OPN has the same quality of tuning as the chips after it. However, due to some technical tricks, the tuning in this cover might be slightly off. The tricks I used sacrifice tuning for more depth and complexity, which is how I was able to get the sound of ~7 notes from 3 channels.