From what I can tell, all the "Internet TV/Radio" support does is add links to streams to the Subsonic page. It's up to your browser to know what do do with them.
I hadn't tried to add a Shoutcast stream, but just did as an example. I went to
www.shoutcast.com and looked for a Metal station, finding Rock Radio 1. The play button on shoutcast's page just plays it right in that window, so I went to the station's web site
www.rockradio1.com and found the direct URL for the player,
http://87.117.202.97:8005/listen.pls
In Subsonic, I go to Settings -> Internet TV/Radio, and fill in all the information for this station. After reloading the whole Subsonic web page, there is now an "Internet TV/Radio" section above my alphabetical music listing on the left side. The station name links to the stations web site, and there is a little play arrow on the left that links to the stream itself.
But that's all it is -- a link. It plays exactly as if you had clicked the link on the station's own web site, and nothing else. It doesn't add to the playlist, or the Subsonic's web page player. As far as I can tell it's not available from Subair or the Android player.
And to me this makes sense, you don't want the radio streams to go back to your server, then out again to your device. All you need here is a 'bookmark' service. Support for this would have to be added directly to Subair and/or Android app.
For the Jukebox however, it's entirely possible you want the server to play a stream. In my case, I run a Subsonic server in the basement hooked to a whole-house audio feed, so I want one stream into the house feed through the whole-house system. Hence my hack to play streams on the jukebox. (And in reality, you could use that to play any file format that mplayer supports).