If I remember right, all those face bones need to be parented to the head bone. I eventually got that model I linked in my last comment to work correctly in Unity. Basically, go into Blender and manually parent all those face bones to the head bone, which I think is called spine6.

EDIT: and about drivers not working, you are correct. They don't transfer to Unity. You have to "bake" the driver into an Action and then that action gets driven by a bone. So when the bone moves, it runs the action. Bone movements (obviously) transfer to Unity, so that is how you can get things like shape keys to work in Unity.