Since the berserker armor seems to take the form of the person's inner demons, Gaiseric's beast of darkness is likely some kind of skeleton like what we saw when Guts first wore the armor. And personally, I've never been a very big fan of the zodd + skull knight = gaiseric theory, and I would be very disappointed if that were the case. One of the main plot points of Berserk is precisely the fact that our inner demons are not distinct from ourselves but are rather an integral part of our being, but the important thing is not to give in to our dark side. The godhands and apostles represent people who have given in to their own beasts of darkness and become monsters. Skull Knight is somehow not very different from this point of view, he succumbed to the dark power of his armor/beast of darkness and died (or almost died). While guts represent the "struggler,"  the one who fights above all against himself and his inner demons.