Did you mean OSX 10.11? You see, OSX 10.1 dates all the way back to 2001, long before Apple switched from the PowerPC architecture to the Intel x86-64 architecture.
At any rate, you wouldn't want to deal with that 11-year-old relic nowadays: It is only 32-bit capable on the software and kernel side. All Premiere Pro versions since CS5 require full 64-bit hardware and software support. Therefore, you will not be able to even run Premiere Pro CC at all on that particular Mac Pro.
He says it's running 10.11 with Intel processors that support 64-bit.
Should I have him download a trial version and send me proof?
I've run Premiere Pro CC 2018 on a configuration similar to the one listed, on a Mac Pro 1,1. With the help of a decent graphics card it has worked surprisingly well (though on the slow side) for many years for casual 2K video editing, but at this point in time, I would not recommend going down that path.
First, you have to understand that is a system for tinkerers. A Mac Pro 1,1/2,1 does not normally run any OS X beyond 10.7 Lion, the last OS Apple officially supported on it. To upgrade the system further requires a well-known workaround involving a moderate amount of technical knowledge. The Mac Pro you are looking at is obviously using that workaround. If you ever have to reinstall the system, you need to understand the workaround because an installer for OS X 10.8 or later will refuse to run on that Mac.
At some point OS X 10.11 will offer you security updates. This used to be fine, you run it and reboot. But a few months ago security updates started appearing that would put a Mac Pro 1,1/2,1 into an endless reboot cycle that you can't get out of without a second technical workaround. (Remember, 10.11 is not supported on these Macs.)
OS X 10.11 is at the bottom of the compatibility list for Premiere Pro. In the next year or two it is very likely that many applications will drop support for 10.11, and you can't upgrade a Mac Pro 2,1 any further. At that point you either don't upgrade your software, or you're already back to shopping for another Mac. Also, it is expected that Apple will soon stop issuing security updates for 10.11. I recommend finding a much newer Mac to run Premiere Pro, especially if you want to have a good experience, to meet professional deadlines, or even just to be able to play back 4K video.
Also, Premiere Pro (for me) is not correctly importing or relinking to MP4 files on the Mac Pro 1,1. This was supposed to be fixed in the last update, and it works fine on a newer Mac running macOS 10.13.6, but not on the old Mac with OS X 10.11.6.
Although my Mac Pro 1,1 has been a usable Premiere Pro workstation for me in the past, it is now too much trouble to maintain even for casual editing. I have switched over to using Premiere Pro on a newer Mac.