Does Hiddenblade draw still happen when Guardian Angel is used?

Yes, the controller of the unit targeted by Hidden Blade will still draw 2 cards if Guardian Angel is used to save it.

Ruling

When Hidden Blade resolves, it checks if its target is still a legal target on the battlefield. If the target is still on the battlefield (even if the "kill" effect is replaced by Guardian Angel's effect), the spell successfully resolves, and the controller of the unit is established, allowing the draw effect to occur.

Sequence

1. Hidden Blade is played, targeting a unit on the battlefield.
2. Hidden Blade resolves. It attempts to kill the target.
3. Guardian Angel's replacement effect triggers, replacing the "kill" event with "Heal me, exhaust me, and recall me."
4. Because the unit was a legal target on the battlefield when Hidden Blade began resolving, the spell successfully completes its resolution.
5. The controller of the unit draws 2 cards.

As noted in RiftJudge FAQs (such as FAQ #5700 and #4899), Hidden Blade does not require the unit to actually die to trigger the draw; it only requires the target to be valid on the battlefield when the spell resolves so that the game can identify the unit's controller. Since Guardian Angel keeps the unit on the board (or processes the replacement while the unit is still considered a valid target on the battlefield), the draw still happens.