Just to clarify this point: Like every Debian or Raspbian your can easily assign static IPv6 network details on DietPi. dietpi-config network setup has no option for it, as SLAAC works in very most cases and it has hence nearly never been requested, but you can create your own /etc/network/interfaces or better e.g. /etc/network/interfaces.d/ipv6.conf (any filename works) to configure static IPv6 details or DHCPv6 or SLAAC explicitly for any network adapter.
The underlying default network config is done via ifupdown and its configuration file(s) /etc/network/interfaces(.d/), default on Debian and present+initialised on Raspbian as well. And of course any other network stack can be installed and configured.
On the matter of whether is worth it, especially when your ISP is not providing a static IPv6 address and/or you don't want to reach each network device directly without NAT from WAN, I don't see a need to bother with IPv6 in the LAN. SLAAC usually works fine to allow every device doing IPv6 requests to WAN and Pi-hole can resolve hostnames to IPv6 addresses while being contacted via IPv4: The DNS connection protocol version has nothing to do with the resolved IP protocol version, but I think this has been stated above already.