Grasp. If a roller strikes the same foe with both of its attacks in the same round, the roller grapples the foe and attempts to pull it in two. The foe (or a friend of the foe) can attempt a Bend Bars/Lift Gates roll each round to break free. Each round the foe remains in the roller’s grasp, the roller automatically inflicts its maximum possible damage.
So back to no rend, but rather Imp Grab and natural weapon damage.Yeah, it sounds more like a mauling sort of effect. It grapples, then tears, rather than getting a free tearing every time it hits with both attacks.