when a close-combat HSS attack is being made against a character with Impervious does the player get to roll their impervious for each successful roll and is it also true that the rule of three applies to thge defense of a character being attacked by HSS attack?

no you roll it once at the end of the attack

And yes, it's true. The rule of 3 applies to the DV of the target of a HSS(2) attack.

whoops! missed that part of the Q! I read too fast..