I think... the sneak attack is just the sneak attack dice. So you get sneak attack damage as one hit, your main hand, and then offhand. I could be wrong.
Take a look at my thread discussing sneak attack, it shows a gif of sneak attack in action. sneak attack is indeed treated as it's own attack using the hit roll of the original attack.
http://forums.larian.com/ubbthreads.php?ubb=showflat&Number=684282#Post684282But on the topic of multiple attacks, yeah rogues can use their 2nd bonus action from the theif subclass to do a second off hand attack, according to normal 5e rules you are not suppossed to be able to do that, but in the Alpha rogues can do a lot of things they arn't suppossed to be able to do lol.
