as a fixed volume is pushed deeper in the water, does its bouyancy increase?
No it decreases as the "volume" is reduced (a little bit in the case of a cat hull as it does not squash much at a few feet of depth). So no.
My view is that the drednought bows do not reduce pitching in the way most understand; they still dive as much as a vertical bowed boat would (with the same below water profile) but because the foredeck is a /\ shape the water is shedd more quickly and so there is less tripping happening.
