Additionally several screen readers have been tested, Fangs, NVDA, WebAIM and ChromeVOX.
Moodle follows W3c's recommendations to providing the best level of support possible for screen readers and other accessibility tools, however as each tool provider handles things its own way and slightly different than others support can vary depending on each tool.
Additionally this response is regarding the Moodle LMS specifically and not the courseware. Moodle Quizzes and PDFs will work, however SCORM files can vary hugely depending on the type of content and the machine it is running on. Ultimately there are no guarantees that every SCORM will work perfectly with every screen reader as SCORMs made in Flash will not work and some HTML5 content will not read correctly, the best option is to test specifically with the exact version of the tool you are using as support can vary in each version of the tool.