You can look it up: A whistle-blower is a person who exposes wrongdoing. It’s not a person who simply asserts that what he has uncovered is illegal or immoral. Whether the actions exposed by Snowden and Manning constitute wrongdoing is hotly contested, so we should not call them whistle-blowers on our own at this point. (Of course, we can quote other people who call them whistle-blowers.)
A better term to use on our own is “leakers.” Or, in our general effort to avoid labels and instead describe behavior, we can simply write what they did: they leaked or exposed or revealed classified information.
Sometimes whether a person is a whistle-blower can be established only after the revelations have sunk in, depending on what wrongdoing is confirmed or how public opinion eventually develops.