Final answer:
Stateful DHCPv6 servers provide additional configuration information such as DNS server addresses to IPv6 clients, but do not assign subnet masks, default gateways, MAC addresses, or hostnames.
Step-by-step explanation:
Stateful DHCPv6 servers not only pass out IPv6 addresses but also deliver additional configuration information to IPv6 clients. When it comes to what else stateful DHCPv6 servers provide, the correct option from the list is 2) DNS server addresses. These servers do not typically assign subnet masks as IPv6 uses a fixed subnet size for most purposes. The function of a stateful DHCPv6 server is to maintain a record of the assigned IP addresses as well as to distribute information such as DNS server addresses for domain name resolution, which is crucial for navigating the internet. They do not manage default gateways explicitly because each IPv6 address contains the routing prefix which implies the default route, nor do they concern themselves with MAC addresses or hostnames in the context of this question.