I live in New Orleans part-time and evacuated the city a couple days prior to Katrina. Before I left the city, I locked my home’s doors and checked that the doors of the apartment were locked.
When I returned the front of my house and every other house in the city had spray painted markings left by Guard indicating what was found in the house. There were markings for dead people, live people and animals dead or alive.
And, the doors were unlocked and nothing was taken.
So yes, all houses were entered but they did not attempt to confiscate all guns.
But they did confiscate a heck of a lot of them. They left no receipts, and even after a Federal court ordered them to return the guns, they did not return them. They required you to have a bill of sale, or other proof that they were yours. Of course in many cases, that proof was somewhat soggy and unreadable, or just gone. They kept no records of which guns came from where, in which case a driver's license would have sufficed to prove that they came from your house.