The SM's appearance is a close-up/zoom-in of his torso/chest.
Is The Rock really hyping a few secs of SM's chest as a SM's cameo? Or we should just watch this thing in theater this Oct. to see if there's more past this close-up saved as a surprise.
It's not like WB would ever let the like of Randolph, Walsh or place like 4chan or Reddit ruining such reveal.
Surprise or not, either way, after BA in Oct., WBD or the people that made the movie will address the who's playing SM thing one way or another.
Just wait their official statement.