Imbued Fire would never effect a hero through Isolated Hero, because that is a hero card directly affecting another hero. The affect of the card is to increase fire damage by 1, if the damage being increased is the effect of a hero card, then the interaction cannot occur. If the damage being increased is the effect of a non-hero card than it can be increased.
Imbued Fire's boost to fire damage would however make an environment or villain card that deals fire damage deal +1 damage. Whether that villain deals that damage to a hero or not would not matter, it gets the bonus. If a hero is the target of that damage the hero is in no way causing or being affected by the affect of imbued fire, since they are not dealing damage their damage can't be boosted. The villain card effect is being affected.
By any means would not work because while By any Means is affecting the villain, the effect does affect a hero card effect. The hero deals damage, the damage is a Hero Card Effect, it cannot be increased by a hero card effect through Isolated hero.
Twist the Ether on a villain would work because damage dealt by a villain is a villain card effect, and Twist the Ether can affect a villain card effect through Isolated Hero.
Summary:
1. Imbued Fire's increase of fire damage could not affect damage caused by a hero card effect or dealt by a hero, but could increase damage dealt to a hero by a non-hero card effect.
2. By any Means is a Hero card, and cannot affect the effect of a hero card through Isolated Hero, therefore it cannot increase damage that is dealt by a hero or hero card effect.
3. Twist the Ether could affect damage dealt by a non-hero target by a non-hero card effect.
Rational:
1. Damage is the effect of the both the dealer of the damage, and the card that causes it to be dealt.
2. Taking damage is not an effect, but the result of an effect of the card and dealer of the damage.
3. The wording of Isolated Hero stops interaction between Heroes, their cards and card effects.
Interesting things: (my answer)
1. Take Down is a hero card causing a villain to deal damage, could it be affected by Twist the Ether? (No, the damage is a hero card effect)
2. Infection is a Villain Card causing a hero to deal damage, could it be affected by a hero card? (I would guess no, since a hero is dealing the damage)