Yes, it is possible to use the DIVI Builder also on custom post types, but not out-of-the-box. This is valid also for custom post types that plugins created, so you can for example use the DIVI Builder even on your All-In-One-Event-Calendar Events or WooCommerce Products. This entry in functions.php of your child theme will do the trick, just replace custom-post-slug with the slug of your custom post. Add another such line if you have more custom post types to use the DIVI builder on. You can find out the slug names when clicking on the main menu item of the custom post type, in the URL as …/wp-admin/edit.php?post_type=ai1ec_event for All-In-One-Event-Calendar or …/wp-admin/edit.php?post_type=product for WooCommerce, just to name two.

Enjoy the DIVI Builder now on all custom post types as well. Isn’t this great? Made me jump in the air when I just found out about it.

UPDATE 2016-04-13: Bringing back the Meta Box

Integrating the DIVI Builder into Custom Post Types did not bring the DIVI Post Settings Meta Box by default. Andrei from the ET Support was extraordinary helpful in diving into a solution to finalize this amazing feature. A few steps are required though. The first is to bring back the Meta Box itself with this code into functions.php. Replace custom-post-slug with the slug of your custom post type:

Now the meta box is back, but Page Layout and Post Title were missing. This code brings back the Post Title setting (it is a bit clumsy because the whole function needs to be copied into functions.php and then a few lines need to be added for our custom post type. Also here replace custom-post-slug with the slug of your custom post type):

And a last thing to do to also bring the Page Layout Setting back requires even the creation of a custom_script.js file in our child-theme folder with the following content, but replace the word slug with your custom post type slug (in this case, leave post-type- in front of it):

And to enqueue the script with the following line into functions.php:

Yeah, a lot of customization, but I am so glad he took the time to figure it out, because using the DIVI Builder on Custom Post Types is an amazing feature, and I hope to see it onboard in one of the next updates. Until then, despite a bit of effort, this solution is not a core-hack but update-proof and complete, thanks to Andrei for his fabulous endurance.