Oracle Linux 6.4 installs and enables the Oracle UEK2 kernel, which is optimized by Oracle for Oracle server systems, but as far as I now, the kernel which starts the installation media is the same as CentOS or RHEL.
The MacPro does not have a PC BIOS and therefore requires boot media with EFI boot support. I'm just guessing, but perhaps the CentOS media supports dual booting BIOS and EFI (UEFI) systems, whereas the Oracle Linux DVD only supports PC BIOS.
I would not bother to install Enterprise Linux on unsupported hardware. Your mileage due to lack of hardware support will vary so to speak. The system will most likely not be reliable or not run with optimal performance. It may even result in overheating or weakening your system components.
I have not tried the latest Linux distributions on old Mac hardware, but according to my own past experimenting in this area the results were not acceptable. I would rather suggest to use Oracle VirtualBox, which runs and performs pretty well under Mac OS X.
I don' t see any advantage, but if you really what to remove Mac OS X and replace it with OL, then perhaps the easiest way is to use the CentOS media and then to convert the system to Oracle Linux https://linux.oracle.com/switch/centos/.
P.S. The MacPro 1.1 was the first Intel Mac in 2006. It shipped with 32-bit EFI.
I ran sensors from a terminal and the fans seem to be normal RPM's but who knows if that is a true reading.
If I cook the mac pro 1,1 no real loss anyways as it is pretty much worthless anyways LOL.
I have Virtualmin running on it right now and it seems stable enough only other tweak has been for it to turn back on in case of power outage that I added to a startup script.
I might just have to run this RIG for a home Server because it is a lot quieter than my other Server running Oracle right now LOL.