You can run it on proxmox if you want to mix non k8s machines onto the same hardware. All my k8s nodes are dedicated to running k8s only though, so there is no reason for me to have that extra step.
I would not run k8s on proxmox so you can run multiple nodes on the same machine though, the only reason I could really see to do that is if you only had one machine and you really wanted to keep your controller and worker nodes separate.
You can pin the pod to a specific node and pass through the USB device path and that will work. But the whole point of k8s is redundancy and workloads running anywhere.
Plus for IOT networks like zigbee and zwave, controller position in your house is important. If your server is more centrally located that may not be a concern for you.
I’ve heard of some using a USB serial over Ethernet device to relocate their controller remotely but i haven’t looked into that. Running this one off rpi for the controller just made more sense for me.