If you can read Chinese, the credits give the triple role away. I can't read Chinese and I watched it and didn't even know he was the Black Cloaked Envoy, and had Quite The Moment when Ye Zun showed up the first time - I would go the 'avoid spoilers as much as possible' route, because I personally enjoyed that ride very much.

As for handling the ending vs spoilers, I recently recommended the show to someone and said that the show, despite being my happy place, wasn't 100% happy sunshine, and whether she thought she might want or need warnings about less happy elements. (She didn't.) Whether that's useful for the kind of intro format you're thinking of, IDK!