Thanks Bduff and 90 caliber.
As I have said before and argued with some here at work, Neri and Clemenza would never have betrayed Mike NO MATTER WHAT. Neri had Mikes absolute trust. If you look at the scene where mama Corleone is laid out and Fredo is hugging Mike, Mike looks up at Neri and Neri gives a very indiscrete nod. He knows what he must do, just by Mikes look. He probably liked Fredo, but a job and an order is not to be denied. Neri's attention to detail and commitment to his work is seen throughout the movie as well as some deleted scene's. My favorite is the casino - Klingman scene. Neri was just the type of character where he didn't have to say much, but when he did, he made it count and you had better listen or pay the consequences.