These scans are in my experience always just that: they read the source and match it against a set of common anti-patterns. I was talking about something that would tell me how common commercial screen readers interpret an arbitrary new construct. If you have a specific reference to something else, please send me a link!
Screen readers often cost significant amounts of money, and are not trivial to "just turn on".
just google relevant keywords https://www.google.com/search?q=accessibility+scan+website
and if you want the full experience: just enable the screen reader and try to use your website with it.
/edit: and i almost forgot: chromes build-in Audit tool in the Developer Panel includes some Accessibility tests as well