DHCPv6 is very definitely used with ipv6 and isps, as DHCPv6-PD is needed anyway to send prefix allocations to the router
DHCPv6 does the same thing DHCP does, just for v6 addresses. This includes pushing domain suffix and dns servers.
There is also Router Advertisement, which tells the discovering client that it is a router, what the prefix is, if there is a DHCPv6 server, and what the DNS is. As an alternative to DHCPv6, the client can set their own address based on the combination of the prefix and their MAC address, the SLAAC address. The way IPv6 routing tables are built, the router can always find a route by asking upstream on the address, and upstream only has to forward downstream on an address.