Whirly, is dynamic rollover more likely when taking off than landing? From your explanation it sounds like it occurs if pilot does not go through the "light on the skids" and "balance the aircraft" actions before pulling collective, rather than just a landing with too much sideways speed.
I guess another way of looking at it is that it is any situation where the skid can present a sideways force high enough to start a roll can become dynamics rollover. Basically the aircraft gets into a situation where if it has enough momentum to pass the static rollover angle so you can't stop it. If it just tilts up, but not quite enough to keep going it goes down as a note in the logbook.
The rotor following the aircraft as it rolls will just help it gain the momentum to roll over.
Mart