As you said, this stream is in MPEG2 format. For you to play this via RTMP (or really anything else) you will need to first transcode it to H.264 video and AAC audio. You can use our transcode command to do this. Something like the following:
transcode source=udp://239.1.1.100:1234 groupname=mygroup videoBitrates=1000k audiobitrates=32k videoAdvancedParamsProfiles=veryfast destinations=test1
This will create an H.264 stream with a bitrate of 1Mbps named "test1".