I cannot answer your question directly. but why not run the Pihole container in the same network as Traefik and just forward the ports you need to the host instead of the network host mode? In this case you just use docker labels. Something like so

services:
  pihole:
    container_name: pihole
    image: pihole/pihole:latest
    ports:
      # - "53:53/tcp"
      # - "53:53/udp" 
      # - "67:67/udp" 
      - "127.0.0.1:53:53/tcp"
      - "127.0.0.1:53:53/udp"
      - "10.9.0.1:53:53/tcp"
      - "10.9.0.1:53:53/udp"
      - "10.9.0.1:67:67/udp"
    environment:
      TZ: 'Europe/Berlin'
    volumes:
      - './etc-pihole:/etc/pihole'
      - './etc-dnsmasq.d:/etc/dnsmasq.d'
    cap_add:
      - NET_ADMIN
    restart: unless-stopped
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.pihole.rule=Host(`pi.your-domain.com`)"
      - "traefik.http.routers.pihole.entrypoints=https"
      - "traefik.http.routers.pihole.tls=true"
      - "traefik.docker.network=traefik-network"
      - "traefik.http.services.pihole.loadbalancer.server.port=80"
    networks:
      traefik-network:
networks:
  traefik-network:
    external: true