Can hero 2 play dodge so that hero 1 gets to power up the attack (in order to kill a lot of monsters)?
Yes. I assume that he is dancing around and distracting the monsters while his partner prepares to unload some massive damage.
Plus: If the OL also plays a dodge card, who may reroll now (since there is only one reroll when many figures dodge)?
As is stated in the Blast Ability: The first dodging player to the left of the attacker.