If I save a unit with the boss from hidden blade, do I still draw 2?

Yes, you still draw 2 cards.

According to the official rulings for this interaction:

When Hidden Blade resolves, its "kill" instruction executes. The Boss's ability acts as a replacement effect that intercedes during this execution, changing the outcome for the unit (recalling it instead of killing it). Because the Hidden Blade instruction still executed and the unit remains a valid referent for its controller, the draw effect still applies.

The key is that the replacement effect changes what happens to the unit, but it does not prevent the Hidden Blade spell from resolving or identifying the unit's controller.