If you can inform the writer of that post, it is incorrect
Ninethgate.se is used for Debian systems, NOT Ubuntu 16.
The Ninethgate.se Jessie repo is currently unusable, but not for the reason you state.
It is currently unusable for any purpose because it does not contain a current PMS package. The package version it currently holds is 220.127.116.1148-b38628e, which we all know by now can no longer be used due to the way Plex currently handles codecs, a decision they made that forced a mandatory upgrade to 1.5.1 or higher.
Historically, when that repo was usable, it was perfectly valid for use on Ubuntu because the packages it provided were bit for bit identical to Plex.tv Ubuntu packages. And the reason that repo was provided was because, at the time, Plex.tv did not provide a debian style repo for their Ubuntu packages. That is to say, @yakumo made that repo available as a convenience to PMS users who desired a debian style repo for use on any distribution that could use the Ubuntu package provided by Plex.tv.