While it shouldn't be that way, Charlie Hebdo definitely puts itself and its employers at risk of violence with its antagonizing covers, cartoons and jokes. The magazine definitely seems to go out of its way to make certain people and groups angry, and it is successful in that. Unfortunately, that resulted in a terrorist attack recently, and it could result in similar attacks in the future.
The controversial messages that the Charlie Hebdo publishers promote are bound to offend and disturb some people, including terrorists. Publishing is a risky business, in part, because of the attention that the media wants to gain as well as keeping an open platform for expression. The employees will have weigh the risks and rewards of working for the publisher.
Charlie Hebdo is probably putting employees in danger with antagonizing covers; however, the publishers have the right to publish anything they want on their covers. Yes, publishing controversial covers may increase the danger to employees, but the magazine may feel a sense of duty to promote free speech. Furthermore, no group has the right to control free speech over others.
The publication of Charlie Hebdo was little known outside its host country until the attacks on employees by terrorist. The publication now seems to intentionally offend to attempt another violent response. Their position could be made clear without deliberately antagonizing others. The publishers seem to put increased recognition of the publication above employee safety.