Had to a make a minor tweak inside dhcp-4.2.4-P2/client/scripts/netbsd in order to get DHCPv6 working on NetBSD 6.0 final:

L282 currently reads:  ifconfig ${interface} inet6 add ${new_ip6_address}/${new_ip6_prefixlen}

Had to remove "add" in order for this to apply the acquired address properly.  ifconfig yields a syntax error otherwise.  Unsure if this affects previous versions of NetBSD.

Thanks,
Tim Dean