It is. Any competition that uses the away goals rule will continue the rule into extra time. (hmm I know there's probably an exception ..but .. it would be unusual).
I do agree with OP though, in this game the away goal rule is unfair, and I'd like to see it scraped. There simply is not enough advantage in this game to playing at home 2nd to even out the rule.
But on the plus side of it, it makes the cups more tactical and encourages attacking football in the away legs .. so I understand why the game has away goals.