I highly doubt Nicky Scarfo ever helped law enforcement in his life. So I'd have to say I believe you're wrong not all gangsters talk to cops.
who's to say he hasn't informed on any competition to his business in his younger days
Who is to say he has?
good point we will never know. like a lot of mob stuff we like to talk about.
But the burden of proof lies with the accuser. If you're going to say someone might of snitched, you should back it up with evidence or a rationale beyond just "well all of these guys probably do it".