The network labels for the Virtual Machine network must be identical across the hosts for that host to be selected as a HA/DRS target for that VM. If host 3 doesn't have the same network label being used in the VM, the VM will not be automatically migrated to that host.
I don't know that having the vmk label be identical is really a requirement. I don't think that makes a difference... just as long as the management vmk's and vMotion vmk's can talk to each other.
