If you have access to Canvas Data in a relational database, you could use a SQL query like the following. This includes every teacher enrolled in a course where there's some New Quizzes submission.
SELECT COUNT(DISTINCT e.user_id) AS teachers
FROM enrollment_dim e
JOIN assignment_dim a ON a.course_id = e.course_id
JOIN submission_dim s ON s.assignment_id = a.id
JOIN external_tool_activation_dim t ON t.id = a.external_tool_id
WHERE t.name = 'Quizzes 2' /* This is the tool's name in our Canvas Data table */
AND s.submitted_at IS NOT NULL /* Filter to completed attempts */
AND e.type = 'TeacherEnrollment' /* This gets custom roles as well as the built-in Teacher role */
AND e.workflow_state = 'active'
