So, unless something has changed, and I am unaware of the change, all characters come with a hand weapon.

If I am using a character which does not have the class of hand weapon I am using listed in their character profile, such as the haradrim warriors, which special strike may I perform?

If no weapon is visible, the models are normally unable to perform any special strikes (although they will indeed count as having a hand weapon, unless explicitely described as 'unarmed').

If agreed upon with your opponent, you may allow all models with no visible weapons to e.g. feint, by the assumption that they'll carry a hidden dagger or knife somewhere.

That makes sense, on both accounts.