Michael definitely took a big risk sending Rocco on that mission because Rocco was identified with him. But he was determined--obsessed--to nail Roth. Rocco dead on the spot was less a threat to Michael than Rocco alive and in police custody. And Michael knew it, which is why he said, "I want it [Roth's plane] met," instead of suggesting a plan that was less risky to Rocco.
In that case Rocco paid the ultimate price and knew so going in. Perhaps that was his way of being assured the Corleones would always take care of his family (assuming he had one) because he died with honor.
