Yes, its necessary to remove the fan clutch and blade from the car to replace the alternator. Others have reported sneaky ways of avoiding the task, but for overall ease and space to work, it needs to be removed.

And to add onto lo_jack's response regarding the nut on the fan clutch, it is a reverse threading nut. So once you have the fan pulley held in place, you want to turn the wrench clockwise to loosen it.