Can traditional CMS/eCommerce be used with a headless platform?

This depends on the traditional platform. With a headless CMS, the key difference is its ability to create different content types and then make that content available through an application programming interface (API). 

If a traditional CMS is able to process API requests it can be integrated with a headless platform. If it's not then programmers will need to process the API requests outside of the traditional CMS, through the use of javascript in the display of the website. 

Understanding what a traditional CMS is

A monolithic or traditional cms is a content management system that stores all of its content in a single database. This means that all of your content, including pages, posts, comments, and media, are stored in one place. A monolithic cms is best suited for small websites with relatively simple content structures. If you have a large website with complex content, you may want to consider a different type of content management system.

Understanding what a headless CMS is

A Headless Content Management System (CMS) enables users to manage and store content without the need for a graphical user interface (GUI). A headless CMS is often used in conjunction with a “front-end” website or application that provides a GUI for end users.

You can learn more about headless vs monolithic in this guide: 

• What is a headless CMS 
• The difference between headless vs traditional CMS 
• What is a decoupled CMS 
• Headless vs decoupled CMS 
• Things to consider when choosing a headless CMS 
• Headless CMS case studies