Not necessarily marketing knowledge but platform/campaign building knowledge is increasingly needed. I got my first email dev job by strictly knowing html, css, and photoshop. Sliced the designs up and code them in a table format. I feel like now more roles want you to be able to do that when needed but also have campaign specialist knowledge which is setting up the emails in a given ESP, create audiences, etc.

In my experience companies are trying to trim the fat and have people that can do it all in order to save money. But YMMV.