Start with an explanation of the levels of 'canon' status, then here is the data on Starkiller -- odds are it will give you all you are seeking.
Wookiepedia itself is not canon, but you can look at the sources on pages to see where data came from (most of the time), and the Canon article explains how the canon level is defined.
And, to make life easier, here is a simple breakdown of the canon categories you will often hear used when you ask Star Warks questions:
(extracted from the Canon article above):
- G-canon is George Lucas Canon; the six Episodes and any statements by George Lucas (including unpublished production notes from him or his production department that are never seen by the public).
- T-canon or Television Canon refers to the canon level comprising the feature film Star Wars: The Clone Wars and the two television shows Star Wars: The Clone Wars and the Star Wars live-action TV series.
- C-canon is Continuity Canon, consisting of all recent works (and many older works) released under the name of Star Wars: books, comics, games, cartoons, non-theatrical films, and more.
- S-canon is Secondary Canon; the materials are available to be used or ignored as needed by current authors. This includes mostly older works, such as much of the Marvel Star Wars comics, that predate a consistent effort to maintain continuity.
- N is Non-Canon.
1/6/15 -- Update: With the acquisition of the Star Wars franchise by Disney, this answer is no longer valid, although it was when the question was asked. That being said, take a look at the above Wookipedia article on Canon; the 2014 Reboot section talks about the changes due to Disney.
On April 25, 2014, a StarWars.com press release confirmed that the films of the sequel trilogy would not adhere to the post–Return of the Jedi Expanded Universe, with further comments from LucasBooks Senior Editor Jennifer Heddle confirming that the EU as a whole is no longer considered canon. The EU has been re-termed "Legends," with related publications remaining in print under that banner.
Since then, the only previously published material still considered canon are the six original trilogy/prequel trilogy films and the Star Wars: The Clone Wars television series and film. Most material published after April 25—such as the Star Wars Rebels TV series and all novels beginning with A New Dawn—is also considered part of the new canon, on account of the creation of the Lucasfilm Story Group, which currently oversees continuity as a whole. Characters under the Legends banner are still available for use as needed, even if events concerning them are no longer canon.
Gven that Starkiller's appearances are restricted to the video games, EU Novels and comics, his presence is officially part of the Legends banner and as such, not canon.