First to clarify that we are talking about live migration via another interface where the KVM HVs are inter-connected?
There are several ways to achieve this.
One is to alter the DNS resolving in a way that the HV hostnames are resolved to the IP’s of the desired network.
Another is to alter the migration script in /var/lib/one/remotes/vmm/kvm/migrate. For one of our setups I’ve appended a common suffix to the $dest_host variable and added DNS records to resolve them. Please note that you need to sync any changes made to /var/lib/one/remotes to the hosts issuing this one-liner:
su - oneadmin -c 'onehost sync --force' .
As usual there are probably other possible ways to resolve this issue, but the above ones I’ve found working for me.