For example, Bisharp has a +2 Attack boost from Swords Dance, if the opponent uses Haze/Clear Smog, will my Attack still be at +2?
First off, Clear Smog wouldn't hit Bisharp.
But, no, it wouldn't as Haze eliminates all stat changes. So meaning if you have a Swords Dance up, Haze technically didn't lower it, it resets it.
Source: Tested on PO.