I don't think so. I would imagine that the word on something as huge as an attempted hit on Michael Corleone in his house, in his bedroom where his wife sleeps and his children come to play with their toys would get around pretty fast. Pentangeli knew about it, and this would assume that so did Pentangeli's men, and in turn there would be a buzz among everyone who was "connected."

This raises a new question, however. Roth had a "plan B" which was to have Michael assassinated in Cuba. To me this means that when they first got to the island, Roth still believed he had hoodwinked Michael. However, by the time Roth did his Moe Green rant and made the comment that if the money wasnt on the table after his nap he would know he didn't have a partner, didn't Roth know that Michael was his enemy? Was his going to the hospital a ruse to hide from Michael? Certainly if he had not gone to the hospital the murder of Johnny Ola would have tipped him off. So when Michael asked Roth who gave the order to kill Pentangeli wasn't he showing his hand?