Yes, curiously that is mentioned in the English trailer, but not the French one, where the focus is on his hatred and anger consuming all - I believe the theme is similar in the German one but I am not 100% about that one. I'd be interested to know what the JP one says. It sounds a bit like poetic embellishment that can be interpreted in many ways.
Regarding any souls consumed to summon Zodiark for their aether, one thing to bear in mind is that he too was sundered. It makes their status something of an unknown, but they could feasibly lie dormant inside him rather than the Lifestream. Frankly, if you want a potent source of soul energy, there is one inside the planet already (and which may extend outside of it into the heavens as well.)
