I can't find it at DLNA.org, either. LG has always claimed DLNA certification as a media player:
http://www.lg.com/us/tv-audio-video/video/LG-ST600.jspJRiver does see the other DLNA devices on my network.
FWIW, here is the "DLNA Profile":
LG ST600 DLNA SINK
http-get:*:audio/l16;rate=44100;channels=1:DLNA.ORG_PN=LPCM,
http-get:*:audio/l16;rate=44100;channels=2:DLNA.ORG_PN=LPCM,
http-get:*:audio/l16;rate=48000;channels=1:DLNA.ORG_PN=LPCM,
http-get:*:audio/l16;rate=48000;channels=2:DLNA.ORG_PN=LPCM,
http-get:*:audio/mpeg:DLNA.ORG_PN=MP3,
http-get:*:image/jpeg:DLNA.ORG_PN=JPEG_SM,
http-get:*:image/jpeg:DLNA.ORG_PN=JPEG_MED,
http-get:*:image/jpeg:DLNA.ORG_PN=JPEG_LRG,
http-get:*:video/mpeg:DLNA.ORG_PN=MPEG_PS_PAL,
http-get:*:video/mpeg:DLNA.ORG_PN=MPEG_PS_NTSC,
http-get:*:video/vnd.dlna.mpeg-tts:DLNA.ORG_PN=MPEG_TS_SD_NA,
http-get:*:video/vnd.dlna.mpeg-tts:DLNA.ORG_PN=MPEG_TS_SD_NA_T,
http-get:*:video/mpeg:DLNA.ORG_PN=MPEG_TS_SD_NA_ISO,
http-get:*:video/vnd.dlna.mpeg-tts:DLNA.ORG_PN=MPEG_TS_SD_KO,
http-get:*:video/vnd.dlna.mpeg-tts:DLNA.ORG_PN=MPEG_TS_SD_KO_T,
http-get:*:video/mpeg:DLNA.ORG_PN=MPEG_TS_SD_KO_ISO,
http-get:*:video/vnd.dlna.mpeg-tts:DLNA.ORG_PN=MPEG_TS_SD_EU,
http-get:*:video/vnd.dlna.mpeg-tts:DLNA.ORG_PN=MPEG_TS_SD_EU_T,
http-get:*:video/mpeg:DLNA.ORG_PN=MPEG_TS_SD_EU_ISO,
http-get:*:audio/mpegurl:*,
http-get:*:audio/mp3:*,
http-get:*:audio/wma:*,
http-get:*:audio/x-ms-wma:*,
http-get:*:audio/mp4:*,
http-get:*:audio/mpeg:*,
http-get:*:audio/wav:*,
http-get:*:audio/mpeg3:*,
http-get:*:video/x-ms-avi:*,
http-get:*:video/mpeg:*,
http-get:*:video/avi:*,
http-get:*:video/mp4:*,
http-get:*:video/x-matroska:*,
http-get:*:video/quicktime:*