My understanding from past experiences in storm chasing is the release of liability doesn't cover negligence. So if they knew something was wrong with the vessel, ignored it and the negligent action resulted in the catastrophe then the negligent action would not be covered by a hold harmless agreement.
So if I took a group storm chasing and had them all sign a hold harmless and we got hit by a tornado then that risk was accepted as part of chasing tornadoes. If I were to drink a 1/5 of vodka and drive us head on into a semi then that risk was not assumed as part of chasing tornadoes therefore I would still be liable.
For a less obvious case, if I was chasing the tornado with a vehicle while I knowingly had a bad tire and did not get it replaced then it could open up some liability. For example, while chasing the tornado the tire blows, vehicle gets disabled and the tornado hits us, I would be liable because if the tire did not blow out then we wouldn't have been hit by the tornado. It was the neglect of the proper equipment on the vehicle that directly led to the incident that otherwise would have been avoided.
So yeah, if the company wasn't negligent then good luck signing a release of liability and then demanding liability for the terms specifically on that release.