Carrie Haggerty asked Google's John Mueller a question I've never seen before, asking if shadow DOMs are okay with GoogleBot and if Google can index the content. A Shadow DOM refers to the ability of the browser to include a subtree of DOM elements into the rendering of a document, but not into the main document DOM tree.
John Mueller's response was simple, test it with the Google Fetch and Render tool within Google Search Console and see what is rendered. But John said off the top of his head "it should just work."
Test it with Fetch & Render - it should just work.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) August 2, 2017
But the core answer is, when in doubt, really - just use the fetch and render tool and you will be able to see quickly what Google can see and what it cannot see.
Forum discussion at Twitter.
