It goes without saying that neither Arminians or Calvinists, on the surface, would seem to fit this description. Beneath the surface, however, I think their positions are essentially in agreement with Agnosticism, or at least ought to be, if followed to their logical conclusion.
Any system that ascribes to God behavior that, in humans, would be evil, and yet calls it good when applied to God, is essentially saying that for God good, as we know it, may be evil, and evil, as we know it, may be good. But if God being evil, as we understand it, is consistent with His being good, as we understand it, then could we not argue that His being truthful, as we understand it, is consistent with His being deceitful? Is it not possible that there's some subtle way, inaccessible to our finite minds, of reconciling these two apparent opposites? In the same manner, is it not also possible that God's existence is consistent with His non-existence? In other words, if we apply to God things that are logical contradictions, by our lights, then we confess that our light is insufficient to investigate God, or even properly understand and interpret His revelation, for anything He reveals may mean the opposite of what it seems to be saying. Hence, the only reasonable recourse is to admit we can know nothing of God, including whether or not He exists. And this meets our definition of Agnosticism.
That doesn't mean there cannot be things about God that are beyond our understanding. Certain things are indeed beyond the grasp of our finite minds. But I am discussing concepts that we can understand. For instance, we know it is morally better to be good to our children than to be bad to them. There is no mystery here; nothing beyond our finite understanding. And yet the Calvinist suggests that God, in dealing with His children, is just and good in treating them as badly as He possibly can. How do they justify it? By claiming God is not our Father; He's only our Creator! In other words, they seek to absolve Him of the lesser obligation by appealing to an even greater one. Again, there is nothing mysterious here. Not even remotely. Hence, if this be true, then we have to admit that it's entirely possible, even probable, that God's logic is so removed from our own that we may not trust our senses to apprehend it properly. Consequently, God's up may be our down; His truth may be our lie; His good our bad; indeed it's possible that His idea of existence is consistent with our idea of non-existence, so that when God says He exists, what He really means is that He does not exist. And if this is true, then we must admit, with Job, that we “cannot arrange our case for we are in darkness.” But more than this, we must also admit that we cannot understand anything about God due to this darkness. He is a mystery, plain and simple.
And if God is unknowable, than we have, once again, met our definition of Agnosticism.