Other way around. Both the game and Countdown to Darkness lead to the Nibiru mission; however, CtD is presented as a "standard" mission, while the game is kicked off by a distress call (presumably diverting them while on the way to Nibiru from Countdown to Darkness).
Okay, I was wrong. Thank you for correcting me.
Orci has said that the current comics are canon. Not sure about the video game though.
He has said both the comics and the video game were canon. However, he has taken those statements back since then. As much as I wish the comics were canon, they're unfortunately not. Plus, it would probably take all the members of the Supreme Court and those above them at Paramount to make a change to canon policy not just the word of one or two people involved, even if it is Bob Orci.