I've done this and the only things that I see in my Plex app are locally-stored contents and my TV channels (delivered over IP by my ISP).
So as far as Plex is concerned, this is an HDHomeRun tuner + XMLTV EPG.
I can also tune directly into any of the TV streams using VLC, in one of three ways:
1. raw MPEG transport stream over UDP multicast
2. same stream over HTTP (via udpxy)
3. my ISP's transcoded HLS stream (lagging by a few seconds and missing certain features)
I picked Emby for many reasons and one being local accounts I control. Plex pushing you to use their accounts (and then pushing streaming content like this) just wasn’t an option.
Also plex suffered a hack that compromised online account user logins.