There were several rumors about that port, but no official confirmation. Yet someone has just been able to play it on Steam today, probably as a selected beta was released, or the public release actived on some servers. Anyway, you should be able to kill zombies on Linux very soon, with Dead Island.
EDIT 25 October 2014: The game is now available on Steam for Linux users. Here’s a video capture shared by Xpander (thanks for the tip). I also confirm it runs very well on my side.
ORIGINAL STORY: Note that the port is indeed confirmed if we look at SteamDB:
The game icon does not show yet in the Steam client for Linux, but at the same time there’s an ongoing sale for this game at something like 4-5 USD depending on your geography, until the 27th of October.
Note that Dead Island had a very successful marketing campaign back in 2011 because of its perfectly executed trailer (which did not have much to do with the actual game).
Some fans actually did a live recreation of that trailer, which was masterfully done as well:
And Goat Simulator did a spoof of it when they launched their game. What did you expect from Coffee Stains Studio ? :)
Anyway. Dead Island is certainly not the bestest Zombie game ever, but it was decent and certainly worth 5 USD. Note that we still do not know if it’s a native version or a wrapped one, but in any case it should run well on recent hardware.