Yes the container will have it’s own IP, but wouldn’t that mean that nzbget would also not work if that was the case?
The setup is running on a Synology NAS, so pihole exposes port 43 (plus the other ports) on the NAS, other devices on the network work great.
I was able to get nzbget working (also on the same docker network on the NAS) when I configured DNS to point to the docker network interface on the local system (172.17.0.1). As expected, it fails when DNS was configured to use the IP of the NAS itself.
I’ll do some reading on macvlan though, I’ve not familiarised myself with that.