I am having the same issue similar to my WooCommerce Page Builder Plugin.

http://dawnthemes.com/support/forums/topic/dt-woosingle-product-dt-woo-cart-add-elements-not-showing-up/

I have successfully installed the WooCommerce Product Layouts. I opened a new page. When I went to go use Visual Composer and pressed the + Add element button, the DT Woo Commerce tab was missing.

I have recently updated to Visual Composer Version 5.2.1. After updating, I installed the WooCommerce Products Layout plugin.

What can be done to fix this situation? I have attached 2 pictures on this post. Image 1 is a picture from your instructions. Image 2 is a picture of the missing tab on my Visual Composer.