If my opponent (on dredge) goes to flashback cabal therapy sacking a narcomoeba, does it hit their graveyard (triggering Bridge from Below) AND THEN get RFG'd? Does Kalitas' effect skip the graveyard all together, negating bridge from below? Same question for any creature with Evoke..does it hit the yard first?

Kalitas is a replacement effect, noted by the use of the word, "If". This means that the narcomeba going to the graveyard is replaced with the narcomeba going to the exiled zone. Narcomeba never goes to the graveyard and never triggers bridge from below.

If the wording on kalitas was 'when a creature dies and goes to the graveyard...' the when indicates a triggered ability meaning the narco would hit the graveyard, kalitas trigger to remove would go on the stack and bridge from below trigger would go on the stack and both would happen. But since he's worded with 'if' its replaced. Yes, kalitas can help shut down bridge from below.