Just an update. This works with both Divi and Elementor. In both cases, you need to change a setting in the builder to tell it to edit SEO Generator pages.

It's notable that the template page selection doesn't give you the templates available in the themes.

I wanted a full page landing page without a header or footer. To get this is Elementor, I needed to pick the default template, then change the defaults for the entire site to be header and footer free, otherwise I couldn't have a template that gave me a full canvas. Similarly, in Divi, to get a full page landing page without a header or footer, I needed to select the default template and then use the Theme Builder to assign a template with no header and footer. In Divi the visual editor can only be used within the page editor but you can work around it. So...excellent product which could have more clear instructions for Elementor and some improvement for Divi integration but it definitely works.