Hi,
Nothing is officially supported or not with EXOS VM. This is a great educational, training tool, but only - so far - a best effort. I love them and use them all the time, don't get me wrong.
As for the Athlon CPU, I have no idea and I can't test it. It's designed for x86 so it's supposed to work. What version of the Athlon processor are you using? If it's a very old one, maybe you're missing some necessary registers. I'm assuming you have looked into the bios and set all the virtualization capabilities of the CPU?