As of right now, it is up to the adopter to review for accessibility. However, when you make a remix of a book to customize it for you own use, you can use the Accessibility Checker in the Editor to review for any concerns on any pages.
Then, you can use the Accessibility Checklist in the Conductor for your remix to ensure you are keeping track of each page and any of the multitude of checks your institution requires.
We are working on a bot to go through and fix common issues. Check back here for any updates on this and any new ways we will tag any pages with updates or persistent issues.