Hello, if your question was to PLAY or ADD a HLS Stream into Plycast Playlist, let me share you my experience.
I don´t know if this method work with HLS stream.
But in my case, I was in need of programming or schedule a playlist with our own content, but we also need to add or be able to play at our playlist, stream media live from other streaming partners.
I With the SEND COMMAND plugin was able to add it to my playlist
and with the next command play the live streaming from our streaming partner.
PLAY 1-1 [URL] "https://XXX.akamaized.net/hls/live/2015530/XXX/XXX/streamPlaylist.m3u8!"
Don´t know if you were looking for something like this hopefully hope your find or workaround what you need.
I Hope this will be helpfull for someone, sorry for my english.