Following up on this, for the benefit of anyone else who faces the same problem, I'm happy to say we have VMs reporting IP addresses with latest Kali now.

I've not managed to fix the fact that it is taking Kali a lot longer to report IP address (compared to the last version that shipped with ovirt-guest-agent, which reports IP addresses almost instantly on boot), but I extended the time out to give a lot more time for the VM to get an IP address (it is taking around 5 minutes), and also needed to add exception handling to the Vagrant oVirt plugin, around accessing the nics_service, which was throwing an oVirt error after a few minutes "Can't send request: Failed sending data to the peer", after allowing those errors to be ignored during the wait for an IP to be reported, it does eventually report the IP address, and other guest information. VMs are now reliably building again (albeit taking a little longer).