The USB SuperDrive normally won't work with the older (pre 2013) Mac Pro, but if you use the Terminal command:
sudo nvram boot-args="mbasd=1"
then restart, it may work. Connect directly to the computer, not through a USB hub.
Resetting PRAM will clear the setting.
Have you tried VLC?
http://www.videolan.org.
With most DVD drives, it will play DVDs even if the disc and drive region settings don't match.
If you do need a second drive, you can install one internally. Internal drives can be set to different regions.
http://store.mcetech.com/mm/merchant.mvc?Store_Code=MTOS&Screen=CTGY&Category_Co de=STORDVDRWINTMP
https://eshop.macsales.com/shop/optical-drives/superdrives/
I have two MCE Blu-ray drives in my 2008 Mac Pro, set to regions 1 and 2.