To believe the the NSA has broken SHA-2 would be to believe that the NSA found something the entire rest of the world combined hasn't found for twenty years.
Why would the NSA or any other intelligence agency reveal that it had cracked/compromised an encryption technology? Wouldn't they keep it a secret as long as possible, to collect as much damaging information as possible, just as the allies did in WWII?
They may not however SHA-2 has been in a use a long time and a vulnerability would leave financial and communication systems in a country vulnerable. It would be highly risky for say the UK intelligence community to discover a flaw and then not warn UK companies. If agents for one state can discover the flaw so can another. It would be like someone building a fortress out of TNT because they believe only they know it is explosive. To my knowledge no governmental agency (or non-governmental entity) has published any warning about the security of SHA-2 even without disclosing a specific flaw/weakness.
It really isn't accurate to compare encryption in WWII (a niche application over a small period of time with no non-military usage) to SHA-2 (one of if not the most widely deployed algorithms in the world used over an extended period of time in pretty much every aspect of the global economy). Wouldn't you agree?