The IPv6 routing table is usually based on the information in the IPv6 Router Advertisements (RAs) that a box received. RAs are part of the Neighbor Discovery RFC4861 standard. The RA contains a lifetime value for creating a default route. If the lifetime is larger than 0 the router sending the RA will be used as a default route.
There is also an extension to RA messages in RFC4191. With this extension an RA can also contain more specific routes, each with its own lifetime value.
The DHCPv6 server does not create or need extra routes. All routing is done through the normal routing table. The DHCPv6 server is a normal server and can be pinged like any other box, if your routing is set up properly of course.