God using an evil person as an instrument of punishment

God actually used the evil Nebuchadnezzar as an instrument of judgment on Tyre, Judah, and Egypt? It's hard to believe that on occasion God actually used non-believers to accomplish his purposes. For instance, he used Rahab to assist the spies sent by Joshua to assess Jericho"s military capabilities. Didn't God also use the Witch of Endor to thwart the plans of enemies to attack Judah?

Everything in creation is meant to unite and serve their Godly purpose. Also, God can do whatever He wants, however He wants. That's the most elementary belief in monotheism.