At Gen Con I saw the displayed Massive Darkness minis and they looked awesome. They also looked to be the harder GW-type plastic (like in Silver Tower) rather than the softer, Zombicide-style plastic. I talked to a CMON rep to confirm this and he said he thought those were production plastics but wasn't sure. It didn't look like resins like the Rising Sun minis did.
Sure hoping for the harder plastic for this game.
I doubt if it's ABS, or styrene injection molded plastic, honestly.
I would wager it's the same PVC, just with more plasticizer in it, thus making the plastic stiffer.