Smart content will not show any item unless it has been setup to include metadata with the product which is generally found in: ContentLibrary/Runtime/Support

Most Renderosity products will not have metadata and will need to be found via the normal content menu unless the product otherwise specifies.

Generally all content is made up of a top folder which can be called a number of things e.g. My Library, My DAZ 3D library etc And the actual product contents below that. You need to merge all products under your own top folder what ever it is called without nesting the top folder if included with the product.

Hope this helps