with labels you can use an attribute value to define your rotation (but I think that you'll need Maplex for that)
With annotation, you can add the annotation editing toolbar, and rotate your annotation with the Edit annotation tool
Click the Edit Annotation tool Edit Annotation on the Editor toolbar and select the annotation.
Right-click and click Rotate Mode, or press the R key. The pointer changes to a rotate symbol.
Click and drag the text to where you want it placed. The text rotates freely about the selection anchor. You can also press the A key to enter a specific angle for the rotation. You can change the rotate mode pivot point by dragging the selection anchor to another location. To rotate and snap the annotation to another annotation or feature, turn on the secondary selection anchor. Press the S key to toggle this secondary anchor point on and off. You can move the secondary anchor the same way you move the selection anchor. When you have positioned the text where you want it, right-click and click Finish Rotate Mode, or press the R key again
