If you use an LED compatible flasher, you don't need resistors for the turn signals, but you will probably need one on at least one brake light to allow the cruise to work. I only installed one load resistor (the left side) and my cruise control works again.
Needing a load resistor on the brake lights entirely depends on the way the engineer designed the circuit for the tail lights.
If they built in a full wave bridge rectifier for the brake light circuit (that is what makes the any of the aftermarket LEDs polarity insensitive, and allows the alternating flash feature of the side maker lights up front when you have your parking lights on), you won't need it.
If they decided to save a few cents on each light, you will need one.