O.K. I tested it on Nethserver 7.2.1511 Alpha 2 and all is working well.
Notes:
Make sure on the script to change to the latest plex server version.
- A plex User has to be created before installation of the server.
 - Log in via your network via samba and create a folder in the plex directory called movies, add a few files. Make a folder called tvshows, add a few files.
 - Connect to your server via browser http://192.168.1.XXX:32400/web/
setup your servers name, and all info it will ask for - The plex files will be found in /var/lib/nethserver/home/plex/
check that your server is running on nethserver by looking in the services window. 
Also a script for upgrading would be needed since PLEX upgrades very frequent.
CHECK FOR UPGRADE  Button.
Thanks