When you create a catalog connection in SharePoint 2013, the following items get configured for you automatically:
- Result Source
- Managed Navigation
- Catalog Category Page
- Catalog Item Page
When using BCS External Content Types, you have to configure all of the items above manually but it is definitely possible. These are some high-level steps:
- Create the external content types, make sure to set a Title field and default action url
- Crawl external content, create new managed properties as needed
- Create result sources by building search queries that only returns items for specific external content types
- Create catalog category and item pages, add and configure search web parts
- Link your catalog pages to site navigation
The following blog post should get you started: Business Connectivity Services, External Content Types and Content By Search in SharePoint 2013 – Part 1. The next blog post will show how to consume the external content on the publishing site using search web parts.