Is there not a mechanism for rotating labels in Dynamic Map Service when a map is rotated? For example, when the map is rotated 180 degrees, the text flips so it is still readable.
The dynamic map service layer is nothing but an image which is exported from your service. It's NOT possible to rotate label within an image. If you want to rotate feature/label then you should think of using AGSFeatureLayer or AGSGraphicsLayer.
