Generally it's AC motors that are negatively affected by a square wave power signal. They run very inefficiently if at all with anything but a pure sine wave. This is why it's not a good idea to run your AC powerheads on a backup system with a cheaper square wave producing inverter.
Without additional details on the design specifics of this 'DC' motor, it's tough to explain why they're talking about sine wave technology, since generally a DC motor runs on DC, that is Direct Current, not Alternating. I mentioned earlier that I suspect it may really be an AC motor since they appear to be feeding it a 3 phase Alternating Current signal from the controller. It is quite possible that the motor is indeed a DC motor & the frequency of the 3 phase AC signal is so high that the motor sees it as DC. Kind of like feeding an LED, which is also a DC device, a high frequency AC or PWM signal. The LED turns on & off at such a speed, that we don't perceive a flicker at all, yet since it is turned off for a nano second, there is some power savings realized over time. Confused yet? I sure as H am. I need to do a little research on running a DC motor with an Alternating Current or PWM signal.
http://en.wikipedia.org/wiki/Pulse-width_modulation