IPv4 and IPv6 are independent enough that the setup you describe should work just fine.
In fact you can even run IPv4 and IPv6 through two different ISPs. That would give some of the benefits from dual homing without needing to work with routing policies or BGP announcements.
But you don't need DHCPv6, if you only have a single network segment.
Your router can advertise itself with a /64 allocated for the LAN. That way SLAAC can be used to configure IPv6 addresses on the LAN without needing DHCPv6. This is AFAIK supported by more clients than DHCPv6 is.
The point where DHCPv6 gets interesting is how does the router know which /64 to advertise on the LAN. Your router could have a DHCPv6 client to request a prefix from a DHCPv6 server operated by the ISP. If DHCPv6 is not used for this, your router would need to be configured with a static IPv6 prefix.