I used the ER605 router in standalone mode first and configured it to block all outgoing DNS traffic except from one IP: my NAS (with Pi-Hole). This way all devices are forced to use the Pi-Hole. Some devices like Chromecasts ignore the DNS setting in DHCP.

This worked great in standalone mode, but this cannot be configured when the ER605 is provisioned with the Omada Controller. The DNS protocol is missing from the list.

So when the ER605 router is configured with the Omada Controller some functionality is missing, which is a shame. 

See this option when in standalone mode (service type: DNS): 

And this option to allow all DNS requests, only from the NAS with Pi-Hole: 

I would like to request that this can be added to the controller. Thanks.