"A case where you have been made aware of a criminal act and if not reported you risk becoming a co-conspirator, guilty of law enforcement obstruction or causing physical harm to a party."

In that case, it doesn't sound like you're offering an ethical reason to speak up -- you're offering a legal reason. On the other hand, in the case of your specific example:

"In one particular case I found a hole in my code that allowed the son of the manager of a hotel to commit extensive financial fraud but I was being asked by the manager to keep quiet about it."

That sounds like a situation in which I would be ethically bound to do something other than just sit quietly by and let the fraud continue.