Here's a guy who went to a monkey park in Takasaki-yama in Japan and donned a monkey park worker uniform for a day to see what it was like. One reason Japan has monkey parks is to get them used to eating food there so they don't invade nearby farms. The monkeys didn't really like having a stranger tend to them, and they made their displeasure known by chattering. They settle down pretty quickly, though. My favorite part was when an experienced worker ran through the park with a cart loaded with sweet potatoes. The monkeys chased after him and picked up the sweet potatoes as the fell off the cart.
I went to a monkey park near Kyoto with my family in 2010. Here's a video: