Can I play a DVD on my iMac with the USB SuperDrive?

Assuming you have a Superdrive compatible with your computer, then yes. If you have not purchased a SuperDrive yet, I strongly suggest navigating to www.macsales.com who has a much better selection of external DVD drives than they SuperDrive. You can even call them and speak to someone that can help you find one that best suites your particular needs.

Yes the Apple USB Superdrive and third party USB DVD/CD drives will play DVD movies. However, they will not play BlueRay or 4K disc's.