This is not my area of expertise, but I think the answer is "Yes - you can have both a dialog and a design_dialog for a component."
See http://docs.adobe.com/docs/en/aem/6-1/develop/components.html#Dialogs
As an example, if you use CRXDE Lite to look in the repository, and inspect the comments component, it has both a dialog and a design_dialog. A comments component can be dragged from the components browser (sidekick). If in edit mode, properties of the component are edited. If in design mode, the resourceType of the component is edited (you can change to a customized version of that instance of a Comment System).
See http://docs.adobe.com/docs/en/aem/6-1/author/communities/comments.html for a description of the two dialogs for comments.
This is a view of it in the repository :
[img]comments-dialog.png[/img]
- JK
