they did a good piece on him on The Ringer. this part jumped out to me because i thought they all did them live.

https://theringer.com/who-doesnt-love-dwayne-johnson-the-rock-undeniables-5084caf1e3d7#.gofc4tvim

Gewirtz first met the Rock when the writer was hired by MTV to script some segments featuring wrestlers introducing music videos to promote SummerSlam 1999. By that time, Johnson had already headlined a WrestleMania, and thanks to his urging, Gewirtz was hired by the WWF several months later. Johnson was eager to collaborate, even as other wrestlers sneered at accepting help from writers.

“You knew that talent was different than the others.”

When wrestlers do their match-hyping interviews backstage, they can choose to record them ahead of time or do them live. According to Gewirtz, almost everybody chooses the former, for the safety net in case something goes wrong. But Johnson insisted on doing his promos live.

“When we did a promo, it actually became an event backstage. The wrestlers and staff would stop what they were doing and gather around the set to watch him. He’s the only person I’ve ever seen that with to this day. It was, ‘Pick up your popcorn box and watch the Rock cut a promo.’”