Visual Composer plugin provides setting options to enable the Visual composer panel under the editor. To check on to this settings go to Visual Composer>Role Manager now you will find the control for Post types drop down, by default it will be active only for the Pages now select the Custom option.
Now different post types options added to the site will be displayed as shown below, now the admin can select/deselect the visual composer plugin on different custom post types, finally apply the “Save changes” button to reflect the changes on the posts.