1. If I create a certification for our mandatory classes (e.g., Defensive Driving or Mandated Reporter), and the recertification uses the same course, how does the class get marked as incomplete when the course completion criteria was met at one point?

For recertifaction of the same course the course is archived and course and activity completion reset (the activity reset depends on the type of activity)

2. I saw another post (Same course in PROGRAM and CERTIFICATION - ID 22395) that brought up a consideration I had not thought of. If they take the course as part of their new hire training, will it show as not completed at some point for them as a new hire? 

If you don't make the new hire course part of the recertification path then the course won't be reset when re certified.

3. Will the new hires who have completed it in the last three months be asked to recomplete it when I launch the certification or will it show as complete for both since it is complete in the course?

The existing course completion record should be applied to the Certification when launched and they won't be asked to recomplete the course.

Regards