You could. But it’s not a direct replacement for the home pod. The speaker is similar to an Alexa speaker and is always on and waiting for you to say, “Hey Siri” or just “Siri”. The Apple TV does not have an always on mic. You’d have to use the remote and press it down. To be fair, I’m not sure if the remote is always listening. I assume not, I’ll check in a bit b
If using the remote only to toggle Siri options is enough then yes you could use it as a sort of replacement.
Used Watchtower on my Synology for a while and it worked well. No issues in that time.
Now I’ve moved to a Nuc and am more experienced with Docker and understand a lot more of it but by no means am a professional by any means, I would say that I wouldn’t use Watchtower. I can definitely see it messing a config up and prefer not to deal with the headache of troubleshooting something without knowing it was an auto update. If I had the time, I may tag the apps I’m happy to auto-update but for now I prefer to have the higher availability.