I don't think we'll see a Sith Trooper class. I think the Bounty Hunter is the opposite of the Republic's trooper. Heavy armor and heavy weapons.
Pirate is not a bad name for the smuggler opposite though.
Here's the way I see it:
Trooper - Bounty Hunter
Jedi - Sith
Smuggler - Pirate/Spy
??? - ???
I'm still curious what the 4th pair will be.