Carlo's lack of vision

Did Carlo really think he wouldn't have to "answer for Santino"? Was he, like Fredo, blinded by his desire for power to really think that the family wouldn't put together the pieces of the puzzle resulting in the assassination of Sonny? Resulting in all roads leading back to him!

The book is pretty obscure when Carlo is talking to Hagen: "The tension in Hagen's voice seemed to have finally alerted him that the news coming up was going to be really important," doesn't seem like Carlo knows all. It's always seemed unlikely to me that Carlo would have a girl call the apartment, it just adds his philandering to everything else. Maybe all Carlo did was tell them Sonny took the Causeway, and all the rest of the plan was a surprise to him, too.

Sort of like Fredo saying:

The novel and the movies make the case that men are blinded by greed and/or lust for revenge, and/or ambition. Rationally, Carlo could never have gotten away with beating Connie twice--the last resulting in Sonny's assassination. But he was blinded by lust for revenge after Sonny beat him up in public. And, he may have been paid off by Barzini, although I I doubt Barzini would have had to promise him anything more than just the opportunity to trigger Sonny's assassination.

For that matter, could Paulie have rationally believed he could get away with "calling in sick" on the day Vito was shot?

Good point. Thirst for power caused the downfall of Carlo, Fredo, and Paulie.

Coppola and Puzo Godfather III
Carlo thinks he can lure Sonny to his murder and somehow end up as Michael's right hand man in Nevada, smirking and smug he had fooled the Corleones

Yes if there is anything to go in question to whether Carlo was aware it's the smirk in the car I'd say.