From a law enforcement standpoint, in a large scale disaster of any kind, you can expect the bad guys to be out in force (that is why the good guys would be armed, right?), and to a peace officer, a man with a gun is a man with a gun. So both good and bad camo'd gun carriers can expect to be looking down the barrels of the badge carrying good guys guns until the good can be picked out from the bad.
Exactly how does one tell a good guy in camo carrying a gun from a bad guy in camo carrying a gun? By first taking the gun away from him, making sure he is no longer a threat of any kind (that often means handcuffs), and spending valuable time trying to get thru on a badly overloaded radio system (assuming it still works), so the dispatcher, in between answering 911 calls and dispatching officers here and there, can run the gun carrying guy thru the computer system (assuming that still works). A lot of this will of course depend on the location. What scares the heck out of people in Los Angeles might be taken as the norm in rural Colorado...
I would suggest to you that in a large scale disaster the good guys who are refugees are going to vastly outnumber the bad guys--exactly like they do during normal times. And anyone who cannot tell the difference between, say, a 70 year old retired civil servant waiting patiently at a checkpoint and an Al Queda member attempting to evade said checkpoint is in the wrong line of work, and probably shouldn't be pointing guns at anybody. I'd be willing to bet that the Al Queda dirtbag would
not be carrying visible weapons and would
not be wearing camo, for a start.