Error installing Nvidia driver for Mac Pro
I will answer my own question. Thanks to the help of the fabulous commenters, I managed to disable System Integrity Protection (SIP) and install the driver. However, because I couldn't see the screen I had a bit of trouble. I booted the Mac Pro into target disk mode, then took an Apple laptop and used a FireWire -> thunderbolt cable to connect the two. I booted the laptop holding down the alt key. I selected the Mac Pro's recovery partition and booted into that. I disabled SIP in there. However because SIP is hardware specific, I had to change the laptop's startup disk to the one from the Mac Pro. I let it reboot, then installed the driver and shut off both computers. I booted both the laptop and Mac Pro up. The Mac Pro had installed the driver and still had SIP enabled. The laptop rebooted from its internal SSD. I hope this helps someone else!