Actually there is a difference between a mil spec '06 chamber & commercial ammo. But the differenc i so small (a slight variation in the shoulder angle) that it doesn't affect anything.
Now mil-spec chambers are usually a bit larger than commercial chambers. It doesn't affect safety but it will shorten brass life. Mots mil-surp rifles were designed with slightly looser tolerances in the chamber to ensure reliable feeding. But it's no biggie except for brass life.
The big difference between mil-surp ammo & commercial ammo for the '06 is the powder burn rate. Mil-surp has a medium burn rate that is used not so much for chamber pressure, but gas port pressure. a really slow or really fast powder will cause excessive gas port pressure & could damage the op-rod of a Garand.
Now personally I only use handloads or mil-surp ammo in my Garand, but there are two commercial companies that make ammo suitable for the Garand. They are Federal (in their Gold Match line) & Black Hills (in some match rifle line they have). I wouldn't use any other commercial ammo - not even the American Eagle stuff - in a Garand because the velocity indicates that it's a bit hotter than mil-spec & probably (almost definitely) is using a slower powder which could push gas port pressures beyond what's cool.
& yes, I know that a lot of people having been using 180 grainers loaded to commercial specs for a long time in their Garands & haven't had a problem. A lot of people like catching a wheel in 2nd or powerbraking when tey leave their friends house. I don't like buying tires or op rods so I try to stick with the ammo the garand was designed for. Or more appropriately I stick with ammo designed for the Garand.
Of course if you have an adjustable gas system then that's another ball of wax...
But yes, there is a difference between mil-surp & commercial chambers, but it's so small that it doesn't affect anything except a gun owners version of trivial pursuit.