KVM I am very familiar with, is core also using KVM? or only Scale?
KVM uses Linux kernel extensions, so only SCALE. CORE also has an equivalent virtualization platform, but it's unrelated and called bhyve.
Is this in response to my proposed setup or just in general virtualizing PfSense?
10G routing and filtering, in general, is a pretty CPU-intensive task especially if you're running Suricata and the likes. Forget virtualizing, even bare-metal systems can struggle depending on the CPU. 1G routing, on the other hand, can be done on a potato for the most part.
As for virtualizing pfSense on SCALE, I have never done it personally, but I do virtualize it on Proxmox (same KVM backend) on the system in my signature. I'd admit that it isn't optimal though. Ideally, you should do what others mentioned and run it as a separate box not only because it's a good security practice to do so, but because updating/servicing the system is a major pain in the neck because the network goes down while I'm rebooting the host and I usually have to cross my fingers and hope the upgrade didn't bork something. It's why I'm not upgrading to Proxmox 8 yet and probably will procrastinate on it for at least a few more months.