The roll to hit part of Akiro's Favor may be a bit vague, but I would interpret it as dealing with any effect that occurs in the Roll to Miss step. Because rolling to miss and rolling to hit are essentially the same thing. Helm of Fear is not one of these effects. With Helm of Fear, you're not rolling to see if you can hit the target, but rather whether or not you can even attack the target due to how intimidating they are. You definitely can not use Akiro's Favor on the Helm of Fear canceling your attack.
I do not have an answer regarding revealing Akiro's Favor after the Roll to Miss step to reroll a failed Daze. My instinct is no, but that's the exact same instinct that told me you couldn't reveal after the Roll Dice step to reroll the attack dice. Arcane Wonders has already ruled against that instinct once.