this was only added to freebsd in April, so we would have to look at what backporting (if any) is required for freebsd 8.
http://www.freebsd.org/cgi/query-pr.cgi?pr=156259it isn't high on my list, as you can configure clients by using dhcpv6 for DNS setting, and RA for address using the 'Other' flag, not 'Managed'. That is supported in windows , mac and linux clients without patches or client ugprades etc (unless it's a very old version of the OS).