I have a Mac Pro 2008 (3,1) with 1 AMD and 1 Nvidia video card. It runs fine (I’m using it now) BUT it won’t boot into the recovery partition.
When I boot and select the recovery partition with <option>, the progress bar gets about 2/3 of the way across, and the three monitors flash (only one is on up until that point) as if they’re going to become active, but the machine reboots instead.
Potentially related (and definitely related to the reasons I want to load the recovery partition): The Ubuntu installer CD and USB stick aren’t recognized at boot.
Before anyone says anything — yes, I’m sure the two cards are getting plenty of power. I have a secondary power supply installed. All of the monitors are hooked-up to the AMD. The Nvidia is used for deep learning.