Well, that is just ipv6 integration, not NTP. Who does your router(s)?
IPv6 Networking FAQ
I have not gone that far into the lan room!

If the local router and hosts on your collision domain do what you do, then it should not be a problem. I seem to recall all IPv4 addresses have an implicit equivalent ipv6 address. Most IP stacks are IPv6 compatible now. Your server should arp for both. NTP usually runs on the payload of the IP UDP packet, and should not much care if grandma is ipv4 or ipv6. The people 2 floors up take care of that. I have not seen any ipv6 used to configure anything, yet, as the local world seems happy to be ipv4 to the casual viewer, or more generally name driven, and we have NAT and intranet 10. and the like behind NAT firewalls, stretching the ipv4 space. Why pay for lots of real IP addresses for the intranet, when there are 16 million for free!