Adding hosts should work normally.
When you choose the domain for your host, be careful:
If you add an own domain (not just a host), your nameserver address must be IP v6, which can be achieved in 2 ways:
+-------------------+--------------+----------------------------+ | Well-Known Prefix | IPv4 address | IPv4-Embedded IPv6 address | +-------------------+--------------+----------------------------+ | 64:ff9b::/96 | 192.0.2.33 | 64:ff9b::192.0.2.33 | +-------------------+--------------+----------------------------+ (taken from RFC 6052, section 2.4)
We require IPv6 because the machine that runs this service only has v6 connectivity.
Updates to external IPv6 DNS servers should work now, see: issue #140