Undead Labs seems to be fully cognizant about. The company's most recent developer blog talked about firearms for its upcoming zombie outbreak games, and the topic proved so irresistible to potential players that a second question-and-answer session has been posted talking more about guns. Whether it's in the console version or the full-scale MMO, who doesn't want to be sure of the highest-caliber destruction one can wreak upon the undead?
The original developer blog talks in depth about trying to balance a realistic feeling with what players will expect from guns, but the follow-up goes into more detail. Gunfire and sounds will indeed attract zombies to players, but the team doesn't seem interested in burying players under mountains of different ammunition types. The guns in question will most likely not be licensed brands, although some licenses are being sought for some more iconic weapons. There also won't be a full spread of exotic firearms in the console game, Class 3, although the MMO version will likely have a wider variety. Take a look at the full set of answers for more details on the best part of zombie invasions -- sweet, sweet hails of bullets.