Do I still draw for Hidden Blade if I retreat my unit?

No, you do not draw 2 cards.

According to the established rulings for this interaction:

• Hidden Blade requires a legal target at a battlefield to resolve.
• When you play Retreat in response, it returns your unit to your hand before Hidden Blade resolves.
• Because the unit is no longer on the battlefield, Hidden Blade no longer has a legal target. Consequently, it cannot identify "its controller" to grant the draw effect, and the instruction to draw is ignored.