As VyOS 1.3-epa1 will be released shortly it's the last change to iron out some CLI design flaws from the past.
We have set system name-server <ipv4|ipv6> to specify a DNS nameserver IP address we wan't to use. We also have set system name-servers-dhcp <interface> which does the same, but the name server in question is retrieved via DHCP.
Both CLI nodes should be merged under one set system name-server <ipv4|ipv6|interface> node - to keep things as they are in real life - we need a name-server.