By the power of truth, I, while living, have conquered the universe.
I was rereading Cryptum and just got to the part where the Didact is brought out of his Cryptum by Bornstellar. There is a particular line of dialogue that the Didact says which made a question click in my mind - could it be possible that a Cryptum is capable of protecting one from the firing of the Halos?
Halo: Cryptum, page 73
He managed one more utterance -- a question. "Has the damned thing been fired yet?"
Now this is pretty shallow evidence for such a large question, one must take into account that the Didact was just revived and may not have been thinking rationally. However, it's evident his memory and hatred of the Halo Rings was still prominent enough for him to ask that question.
In a Cryptum, the occupant would become unaware of the physical world around him, and could remain in a state of suspended animation for thousands of years. Cryptums required an extraordinary amount of force to be breached once sealed. To me, this sounds very similar to the Slipspace Pods from Ghosts of Onyx which were capable of remaining intact if a nuke was to be detonated on it and shielded the occupant from a Halo firing because they were not truly present.
Could it be possible that the idea for Slipspace Pods came from the Cryptums? If so, it seems highly possible that these Warrior Keeps were capable of protecting one against the weapons the Warrior-Servants hated most.