Yes, anyone can purchase the Imperial City DLC...The question you may want to ask yourself is 'Do I really want to purchase the IC dlc?'

While there is some PvE content in Imperial City (quest lines, dungeons, etc.) you can't explore the city and do the quests there without encountering PvP players who want to kill your character. The dungeons once discovered can be accessed without needing to go to Imperial City (so if you are a dungeon runner you might want the dlc for the two new ones).

Bottom line, if you absolutely do not want to engage in PvP or have someone kill your character, then this dlc might not be for you. But if you have the crowns to burn, it couldn't hurt to try it out