Yes, you can use the SETPWM command to set the duty cycle and the frequency of a PWM output. For FMD PLC the frequency is continuously variable between 50Hz and 50KHz so you can create a wave form with very accurate frequency/period, and you can compute the duty cycle required to generate the pulsewidth of your choice.
Are you trying to control a RC Servo with 1ms to 2ms signal? Section 11.4 in the FMD PLC User's Manual Section describes how this can be achieved.