since Servos are practically DC motors with a few extras,
One of the "extras" is a two wire (signal and GND), logic-level control via PPM, so no, you won't need a MOSFET, assuming that we're talking R/C servos here.
The PPM signal is a nominal repetition rate of 50Hz (20ms frame), with pulse width varying from 1 to 2ms to provide the position.