Mac Pro has defenitely some issues what comes to support booting into a different OS Apple has wanted. I had a hack on it that made installing newer OS X versions possible. However, I wasn't satisfied how it performed (time to time it wasn't that smooth as I expected). However, now that I got rid of OS X and boot directly to Linux on a SSD it's silky smooth. Running XPEnology in a VM (4 cores and 4GB RAM) + Win 10 x64 (3 cores and 4GB RAM) on the same time is very smooth.
I understand though, that your comment is related to boot directly to XPEnology --> haven't tried that out. My usecase is such that that kind of setup wouldn't make sense for me. I would guess the main components have been built in the Hackintosh community already, but it would require somebody with required skills to parse them in the XPEnology package.
Now I'm trying to figure out how I could give XPEnology a full access to 3x1,5TB HDDs I have in those internal SATA ports. Haven't cracked that yet even I have searched this forum. If anybody have good pointers I would appreciate those.