Minetest should be possible to install on SteamOS, but its not on steam, so stuff will be a bit harder unfortunately.
First enable generic support to install packages from debian (maybe substitute jessie with testing, as testing may contain more up to date packages):
http://steamcommunity.com/groups/steamu ... 6114274132Then do "sudo apt-get install minetest".
You should then be able to launch minetest with the "minetest" command.
About steamcontroller, there is generic joystick/gamepad controller support, but not for formspecs. SteamControllers _should_ work with that, but i haven't really tried it so I can't say yes or no.
If you want to do serious playing you'll need to either map the keys using antimicro or something similar, or connect a mouse which you use for the formspecs.
Also note that controller support is only present in git builds atm, and not inside the official debian package of minetest. If you want to try the native controller support, you need to get minetest from this ppa instead of official debian sources:
https://launchpad.net/~minetestdevs/+ar ... ily-builds