When you hook up a motor controller like the
REV SPARK or any other (talon, victor, etc) it does not use the power pin from the MXP, just the signal and ground. Which is why it is totally safe to use the pwm in the MXP port using a breakout board like the
MoreBoard.
If you are running servos, I would just use the standard PWM ports instead of buying a $100 + board just for this purpose (unless you need and want it's other functionality.