You can set up usb passthrough through virt-manager or VirtualBox. After you do that, the guest gains complete control of that usb device and it should work/behave like it wasn't even in a vm. 

I can confirm that you can use USB Passthrough to send the USB sound cards to the Virtual Machine which then can use them without limitations. This is also valid for MIDI USB controllers.

I think that with using the USB Passthrough strategy, the PipeWire could be also tested on VMs.

I will update the test cases.

I would be careful with considering such test cases as passed and on par with bare metal tests. When it is routed to a VM, it still goes through the host USB stack. Unexpected things can happen. We might mention it as a testing option, sure, but we should also ask people to append a note saying "usb-passthrough to a VM" or similar to their result submissions, so that we can distinguish them.