In RHV documentation is not specified anywhere that "During an outage of the migration network, VMs will be migrated using the management network." https://access.redhat.com/solutions/70412 https://ovirt.org/develop/release-management/features/network/migration-network Is it possible to have that detail specified somewhere here in the admin guide: https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.1/html/administration_guide/chap-logical_networks
"Outage" is a bit of a vague term. A more precise description of the condition is "when the management network is not properly attached to the source of the destination hosts".
The updated documentation is available in the Customer Portal: https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.2/html-single/administration_guide/index#Cluster_General_Settings_Explained