Batman and Gordon were both part of the decision to hide Harvey's crimes and have him die a hero. Therefore, when the Dent Act was instituted, did Batman, or better yet, Bruce Wayne, try to stop it in any way? Yes he hates crime but he also loves justice, and as Gotham's wealthiest resident he undoubtedly carries significant political clout. However, we don't see or hear anything about his relationship with the act.
Yes, he was totally complicit.
When Batman states that he should take the blame for Harvey's crimes he justifies this move on the basis that the criminals prosecuted as a result of the trios war on crime would remain incarcerated. 'The dent Act' appears to have galvanised this effort, and ultimately those prosecuted were 'essential cogs in the wheel of crime'. Harvey's personal misadventures ultimately do not exonerate those he legitimately locked up