Since we don’t actually have an Adguard, nor have we ever tested our devices with it, I went ahead and imitated your setup with a couple of our devices, I’ve used the RUT956 as the main DNS server, while keeping the RUTX11 as the secondary “backup” option.
I’ve then conducted tests by trying to reach said devices from both, my phone via WLAN & their respective hostnames via a web browser in order to access the WebUI. All of this ended up working as expected.
DNS queries from LAN and Wi-Fi clients are relayed by the RUTC50 router via its internal DNS proxy (dnsmasq). Therefore, upstream DNS servers will only see the router’s IP (192.168.0.1) as the source.
I was able to find an older community forum post with another user asking for assistance for their RUTM10 + Adguard setup, and another user has replied with some proposals for changing the settings, you can look into this, see if it helps or not: AdGuard on RUTM10
Since you have a RUTC50 that supports Docker, you can also look into setting it up on docker too: https://hub.docker.com/r/adguard/adguardhome
Since we don’t advertise our routers as 100% compatible with Adguard, we can’t promise full functionality, and issues are bound to occur, but I believe the posts that I’ve provided should give you more insight on how to set this up. Judging by the other user comments, they seemed to have get it to work as they wanted.
Kind regards,
M.