User Revisioning and Workbench moderation modules only on certain content type
You can most definitely configure only one content type to use revisoning and content moderation. 

For example, once the Workbench Moderation module is enabled, the Basic Page content type can be configured here: admin/structure/types/manage/page

Click the "Publishing Options" vertical tab, and you will see you have the option to check the "create new revision" checkbox, which will enable content revisioning. 

Below that you can click the "Enable moderation of revisions" checkbox to engage the workbench moderation module features. 

You must enable revisioning to enable workbench moderation.  See image below:


For each content type which you desire content revisioning and workbench moderation, follow this procedure.