Really I suppose it depends on how hard and where they hit the rock, was it a failure of of the gamepad that lead to the rock hit? that is, dead controls and drifting (those infernal radio gamepads, amiright) If I remember correctly the whole sub had an outer shroud anyway. how much damage to the outer shroud was done?
Anyway, I don't really want to be the guy defending oceangate, I think a carbon fiber submarine sounds like a monumentally ill founded idea in the first place, and the move fast and break things attitude they employed in their engineering process should have never gone anywhere near a passenger. but at first thought, at the speeds the sub moved I doubt a rock hit would damage the sub. if I had to bet, it was plastic deformation leading to delamination and fatigue.