I am running Version 220.127.116.1149 Plex media server on Ubuntu 16.04. My audio music files, a mix of mp3s and oggs, play fine on my Roku 3 running the Plex client.
I also have activated DLNA on the Plex server and I am using VLC on Android as my DLNA client. I can see the server fine and play mp3 files without issue.
The ogg files do not appear at all on VLC. The directories that have oggs appear empty on the client. The VLC supports ogg. If the ogg file is local, the file will play it without issue. I checked DLNA default protocol info and ogg was not listed. I added http-get::audio/ogg: to the default protocol but still no luck.