I think there is definitely a difference between AO3 lock and DW lock - I would usually try not to even hint at things that were only posted behind DW-lock whereas with AO3 lock I wouldn't hesitate. I think there's an interesting split here between people who think of AO3 lock as primarily a requirement to get an account before you read, and people who think of AO3 lock as primarily a way of hiding stuff from outsiders.