In NWN2 a character cannot wield a weapon they do not have the proficiency for.
The exotic weapons include: Bastard sword, Dwarven waraxe, Kama, Katana and Shuriken.
See also see here.
To use Exotic weapons one must have BAB +1 at minimum. In DnD 3.5 a character takes a -4 penalty to attack rolls when using a weapon she/he is not proficient with.