Using more accounts is permitted (although I'm not sure if they updated the TOS on that front) but what you do with them may or may not be allowed.
You are more than welcome to use more than one account at a time, however this must obey the rules of the ToS. This means you are not allowed to AP trade using these to accounts or use an alt account to insult a player of the opposite faction.
AION Free-To-Play – Additional Game Rules
Special conditions for the use of the online games
Unless the Rules allow exceptions, the user may participate in each round of an online game (e.g. world, universe etc.) using one user account only. It is not permissible to use multiple user accounts ("multi-accounts"). Gameforge is entitled at any time at its own discretion to block or delete unauthorised multi-accounts.
Now, it is most of the time tolerated as long as it is not used to gain an unfair advantage or break the game rules. But as stated Gameforge is entitled to block it at their own discretion.
As a clear answer has been given and this discussion took place many many times in the past I will close the thread now