Is there any way to replace the desktop dock app on the Droid 3? Or at least change the widgets/dock area icons in productivity mode?
If you've got a replacement app, you could utilize Tasker for that:


Condition: Docked
Task: Start App [your-replacement-app-here]


On the next docking, you would be asked for the app to perform this action with. Decide for "Tasker" and see if it works as expected. If it does, make it the default next time.

As alternate app you could e.g. use Desk Clock Plus, which might even support this without the help of Tasker.