Anonymoose, I think you have a too manichean view of the Ascians' actions... Or maybe it's me that's wrong, but let me explain my theories.
There seems to be a conflict between Nabriales and Lahabrea, and Nabriales was unhappy of Shiva being defeated but that doesn't mean he is by her side, or plays with her as he would with a puppet. What Nabriales seems to seek is power, to summon Zodiark maybe, but power for himself before anything else. He stole Louisoix's staff without telling the pthers and so... I feel like Nabriales just hated the fact that there were now two people able to counter them.
Meanwhile, Lahabrea (as well as the white Ascian, whom I forgot the name) is pleased because his main foe, Shiva, allied to the dragoons against Isgard, itself allied with the Ascians, seems not to be understood by our character, and still considered a danger to the Light. If Shiva and the Ascians are foes, and we and Shiva are foes, we're in some way allied to the ascians.
Here is my guess : Shiva is, to Hydaelyn, what the Ascians are to Zodiark, a mortal that obtained such a great power that it became more than that. As our hero was denied a part of Hydaelyn's blessing by Midgardsormr, Shiva might have had the same the same fate. But what she did, saw, or whatever after joining the dragons made her Saint Shiva, a being of power opposed to the Ascians. But, if our hero does not follow her path, it may still be quite neutral about the Ascians, and it is often shown that Lahabrea and the White Ascian want us to join them. So, if we keep fighting Shiva, we help the ascians. If we become allies of Ishgard, as it seems we do, we help the ascians.
So I dont think Shiva is being manipulated, I think we are.
But, what's more interesting is that Hydaelyn and Zodiark seem to be the same kind of deity, and, although they're opposed, the white Ascian seems to believe the Echp, granted by Hydaelyn, will make us receptive of Zodiark's way. So we may wonder, what's the Echo ? The abiloty to see what happened in the past, to see the truth. And what's implied there is that the truth, the awareness of the truth, leads to Zodiark. And while Shiva is the embodiment of Midgardsormr, Ascians are Zodiark's and we are still not determined.
Maybe I'm thinking too much, but to me, we are manipulated by all three "divine" entities, Hydaelyn,Midgardsormr, and Zodiark, and the worst may not be Zodiark...
If something isn't understandable, feel free to ask, english is not my native language and I'l typing on my cellphone, so I can't detail too much x)