I've done this many times. So many that I set up the hypervisor (fanless CompuLab PC) to bridge the WAN Ethernet, and all of the possible USB modems (multiple smart phones, and hotspots) on one interface which the OpenWRT VM uses as WAN. With it set up like this, I can simply plug in the correct device and then reboot. No configuration changes required. Over the years I did need to do some minor tweaks to get IPv6 working properly in all configurations, but it's been solid.
Note that doing it this way doesn't require most of the steps in the parent article document. The hypervisor recognizes the network hardware, assigns it to the bridge, and KVM/virt-manager assigns the bridge to the OpenWrt VM as a virtio network device. OpenWRT sees a plain vanilla virtio Ethernet device so it doesn't need any special drivers or configuration.
Note that doing it this way doesn't require most of the steps in the parent article document. The hypervisor recognizes the network hardware, assigns it to the bridge, and KVM/virt-manager assigns the bridge to the OpenWrt VM as a virtio network device. OpenWRT sees a plain vanilla virtio Ethernet device so it doesn't need any special drivers or configuration.