Yeah if you want the best sounding real kit then there is nothing better than a VST, in terms of a TD-9 etc, there shouldnt be a problem. Roland pads reverse the polarity of the secondary piezo zone, although since that is an edge trigger polarity shouldnt matter since its floating, and I *think* they prefer a leading positive on the head for best triggering but not essential.
Since the TD9 was mentioned... I dont have any DM8 pads but I do have some old DM6 pads lingering around, the snare with the gum type edge switch, I just plugged it into a TD-9 module to see what happens, set the trigger type to PD8 and it worked fine, both zones, complete with velocity on the edge.