Zombies in Dead Rising 4 will wear Servbot heads if the My Bloody Valentine Pack is enabled. You can disable this by doing the following:
1. Go to Main Menu
2. Turn the My Blood Valentine Pack DLC off. This is located on the bottom left of the screen.
Note: On an Xbox 360 / Xbox One controller, this is tied to the 'X' button.
3. You will know the DLC is disabled when the red bloody border is not present on the Main Menu.
4. This will disable Servbot heads and special costumes for enemies.