I just installed a stock LEDE 17.01.4 image (lede-17.01.4-ramips-mt7620) to mess with umdns, but it doesn't seem to be installed or used. And I don't see a package for it on the lede server.
My goal is to modify certain services (e.g. mjpeg-streamer) to announce themselves to Bonjour/mDNS clients. Judging by this it seems quite straightforward.