It is probably worth mentioning again, that although “Yoast SEO” plugin does not parse the content written in ACF fields in the backend, and therefore you might be seeing Yoast warnings (traffic lights, whatever), the main thing Yoast is useful for, is to write your meta titles and descriptions, as well as the handy options in the advanced settings for indexing, following and canonical settings etc on the actual posts, and the additional settings for the meta in the plugin settings itself (sitemaps, taxonomy stuff etc, and maybe the Social Media bling if your theme itself doesn’t already offer such options).
The actual feedback advice it provides on the posts on the admin side is just fluff, it doesn’t do anything for your real SEO, all it does is offer tips based on “Yoast Best Practice”.
The content in the fields that is displayed on the front end of the site is read by the search engine spiders (Google, Bing, Yahoo, Yandex, evilspiders, etc), and that is what counts.
So as long as you follow the basic principles of having a permalink that matches your main keyword (as reasonably as is practical), and your Meta Title and Description, H1 Page Title, and Content hold your focus keyword then that is what matters, no matter if it is written in the WP TinyMCE editor, or an Advanced Custom Field.
The Content that cannot be “seen” by Yoast, can most definitely be seen by the spiders, and they could care less about the Yoastie Toastie traffic lights.
Although of course I am not saying it wouldn’t be nice to have the components working well together, it would be nice.. what I am saying, is it doesn’t really matter in real terms, as long as you follow the basic principles of SEO when writing your content. The real value of Yoast is the other admin settings of the plugin.
