Interesting point. Have you had issues with galvanic corrosion on regular anodized aluminium? 

I have bonded to both, and don't notice a difference, though I would agree that hard anodized is better in theory simply because it can be tricky to nicely prep a part without removing a coating less than 0.002mm thick... These days I don't actually bother, I don't like to include ali in the layup and prefer to do secondary bonding with a decent bond gap and sidestep CTE issues that may present themselves.