Is it OK to then use the Support Aura skill to reroll the 1 rolled via Daring Gamble during "Use Skills/Potions/Place Dice" phase?
1. Daring Gamble rolls a 1.
2. Resolve penalty.
3. Roll other dice.
4. Use Support Aura to reroll any 1's rolled, including the one rolled during the Heroic Feat phase.
Yes, as Chris says (of course).
And if you use Support Aura to reroll a Daring Gamble 1 and it comes up as 1 again, you do not suffer the Daring Gamble penalty again.
(There might be other black 1's around, and there is no way to track which is which.)