An access key can be added to ContentPresenter in WPF if you add underscore in the content and set RecognizeAccessKey to true.If the ContentPresenter is inside DocumentHost, the access key is working, but the underscore in the UI is not visible. If you remove the DocumentHost everything works as expected.
The above mentioned framework issue is logged in Microsoft's official feedback portal and can be tracked here: https://connect.microsoft.com/VisualStudio/feedback/details/829049/underscore-of-access-key-is-not-displayed-when-manually-change-the-logical-tree-in-wpf
The problem is caused by the Framework when you modify the Logical Tree. The document host is added as a logical child of RadDocking manually and in this situation the framework is "hiding" the underscore of Access Key. If we do not add DocumentHost as a logical child of RadDocking, bindings with ElementName inside DocumentHost will not work.