You could statically set the DNS address, while leaving the IP address on automatic (DHCP). (I've done that before, but I forget the reason why...) But if you're there, you might as well do it all.
I can say this much:
I have no idea how much it shortens network connections and interchanges but unbound is fast. After the first name lookup, the next is 0ms (from the OMV server's perspective).
When testing, the DNS bench mark utility shows that local resolution is faster than any server out there. Nothing else is even close.
The way I'm configured is;
The router is the DHCP server and the DNS proxy. The router forwards DNS requests to the Pi-hole/Docker. Pi-hole forwards to unbound, on the OMV host. Even with the local links, lookups are a max of 2 ms.
Faster, more secure, and DNSSEC is forced. It's good stuff.