Yes - PWM can be used for controlling DC motors (it's actually the new favorite method among engineers due to the ease of interfacing with microprocessors, higher efficiency, and lower heat output). There are a few things you'll want to watch out for though:
- Electric motors have a bare minimum starting current (and it's usually higher than the lowest running current).
- Thus, when starting a motor it's best to give it a "spike" of current and ramp down to the desired operating speed
Some say they can see a flicker with PWM dimming, but this is usually only true if the longest period of "off time" is greater than 20 miliseconds (or about a 55Hz cycle). Another reason you'll want to check the PWM frequency before getting into the Dimmer module is that if it's in the audible spectrum (20Hz to 20kHz) and the current is high enough on the motor - you may be able to hear it whine. Typically 30kHz PWM modules are the minimum norm for "inaudible" current regulation.