The customization of the built-in dialogs
and RadEditor's source code is out of the scope of Telerik support. It is up to the developer to implement the project requirements and customizations.
I could not tell for sure whether it is possible to replace the regular dropdowns and textboxes with RadInput and RadCombobobx, but if you open a support ticket and provide a sample working project which demonstrates the problem, I could debug your code and if possible help you with the implementation.
Another approach is to implement your own custom link manager
and use the desired controls in it.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed