How to make light dim when another light is dimmed

There was a LAN integration for Hue at one point, but I can’t speak to its availability. Perhaps someone else here uses Hue with SmartThings and has insights - otherwise you could ask in the SmartThings community.

I’m not sure what this means. Reacting to online/offline events isn’t available, but some people have used workarounds to track offline status of critical devices.