As far as I know, it's not something we can simply turn off with a preference - it's part of the "manifest" of the application, and can't be changed once the application has been built. If there had been a way to make a preference, we would have - this is a limitation of the current version of Android, and I hope that it will be addressed by Google. If someone knows of a way to do this, I'm all ears.
However, there is a way to control *which* application is launched when the device is docked. Most devices will launch the "Clock" application if there's no other application that handles the "dock" event. If there's more than one, you'll be presented with a list, and you can choose one, and you can set it as the default.
To clear a default, you'd go to Settings->Applications->Manage applications->(the application) and scroll to the section "Launch by default" and press the "Clear defaults" button. Subsequent dockings will again ask for which app to launch.
I don't have a dock for our Tab, so I don't know if Samsung or the carrier has provided any other dockable apps.