FWIW:
https://packages.debian.org/jessie/docker.io indeed shows docker (aka docker.io) is included in jessie for the following CPU architectures:
amd64
armel
armhf
i386
But, AFAIK, raspbian jessie is NOT using one-on-ne the debian jessie repository, which means docker.io is NOT automatically in raspbian jessie.
However, I also have got a Cubox (with ARMv7), which does use plain debian, so maybe I'll upgrade my Cubox from wheezy to jessie to check if docker.io is installable and usable...
EDIT:
I upgraded my ARMv7 Cubox to jessie, and docker is installable and usable!
