Unraid is installed on a usb drive. Simply create a VM in proxmox passing through all of your array disks and cache disks that you had attached in unraid as well as the unraid boot USB. Make sure the new vm is set to boot from the USB drive. Now boot up your VM and see how it goes.
The nice part is you can back out of this by plugging the USB drive and all of your disks back into your old hardware. Risk is minimal. I think the unraid license key is attached to the uuid of the usb drive, not your computer, so this really shouldn't be too bad. If you're using a SAS controller for your disks, make sure you pass that through to the VM. Better performance than passing through the disks.