Mark Burnett isn't leaking the Trump outtakes because
1) He believes that Hillary will win, and Burnett needs to preserve his relationship with Trump if he wants him to return to Celebrity Apprentice. If Trump returns to the show, he'll bring much higher ratings now that his profile has increased tremendously. Burnett therefore will do nothing that might sabotage his relationship with him for these ratings.
2) He believes that Trump will win, and it's useful as a TV producer for Burnett to have a sitting president as his friend. Who knows what favors a President Trump can do for him as gratitude for not releasing the damaging outtakes.
Either way, regardless of Burnett's true feelings about Trump, whether he'll even vote for him, Burnett will be looking to protect Trump out of his own self-interest.