No, it does not include supernatural interactions
Iron Will resolves around social interactions (see the Social Manoeuvring rules on p188 and later), while Indomitable references "The powers of the
supernatural have little bearing on her behavior." (rather confusing that they describe the character as having an Iron Will), or even clearer:
Any time a supernatural creature uses
a power to influence your character’s thoughts or emotions,
add two dice to the dice pool to contest it.
- Iron Will helps in Social Maneuvering situations (you motivate somebody else to do something for you)
- Indomitable helps against mental influences from various sources
- If a Vampire Dominates you, you better have Indomitable.
- If he just Persuasions you, you better have Iron Will.
- If he uses Majesty while trying to Persuasion you, you better have both .
Do note that his Persuasion attempt will have various steps, in one of these steps he can augment himself by using a supernatural ability (such as Majesty or Dominate) to give himself a boost (or just trying to shortcut the entire thing by using Majesty 2). Indomitable will help against the use of the supernatural ability, while Iron Will boosts your defense against his entire Persuasion attempt.