If I use a Tactical Retreat on a unit, after I use the Baited Hook and target this same unit, does it save the unit? And does the Baited Hook still occur?

Yes, the unit is saved, and Baited Hook's effect only partially resolves — you'll look at 5 cards but play none.

Here's how it works. Tactical Retreat creates a replacement effect on the unit. When Baited Hook resolves and tries to "Kill" that unit, Tactical Retreat intercedes and replaces the kill with a heal + exhaust + recall. Since the unit was never actually killed (it never went from board to trash per Rule 415.2), Baited Hook finds no "killed unit" to reference for its Might value — it returns null. Per Rule 359.3.e.12, null + 1 is still null, and no unit has a Might of null, so you cannot play a unit from the top 5. You'll reveal 5 cards and recycle all of them.

The unit ends up exhausted and recalled to your base, alive.