I remember someone telling me once "Kid if you get the right kind of pressure you can't trust anyone." The threat of death is definitely that kind of pressure for most as it was for Joe Valachi.

Think he was a rat or just a victim of Genovese's paranoia? or both?

I personally find Genovese to be one of the most detestable figures in the history of organized crime in the 20th century. None of his peers liked him or trusted him. If it would've been only the law after him I think Joe Valachi would've stayed silent. With no real chance to kill Vito I *think would've done the same.