The "docker" package in Trisquel's repository is not what you want:
$ apt-cache show docker
(...)
Description-en: System tray for KDE3/GNOME2 docklet applications
Docker is a docking application (WindowMaker dock app) which acts as a
system
tray for any desktop environment, allowing you to have a system tray without
running the KDE/GNOME panel Docker was designed to work with Openbox 2, but
it
should work fine in any window manager.
(...)
I have never heard of any freedom issues pertaining to Docker. I believe
Docker's developers can be trusted. They are administrating the PPA (your
first link). There is no additional third party you would have to trust if
you decide to use the PPA. That said, it is possible (but not likely, imho)
that Docker's developers do not use the published source code to build the
.deb package but a version with, maybe, malware. If you fear that, build from
source.
