Assuming the Garand is in good condition, I would think that it should handlecommercial loads, assuming proper overall length of the cartridge. I've read that the bullet should be under 173 grains, so 125, 150, 165 and 168 grain bullets should work well.
The conventional wisdom on the M1 is that bullet weights between 147-175gr using a propellant with a burning rate between IMR 3031 and IMR 4064 is ok for the gas system.
The gas and operating system on the M1 relies on the timing of the bullet leaving the muzzle and a fairly narrow pressure curve to function properly without overstressing the parts. A faster burning powder might not fully cycle the action, and a slower burning powder will put too much stress on the oprod- potentially bending it.
Commercial ammo might be ok, but then again you don't know what kind of powder goes into commercially loaded 30-06- my guess is that its something similar to IMR 4350. There aren't too many people around anymore that know how to repair and reset the curvature of an M1 oprod, and spare parts will only get more scarce.
I only shoot handloads through my M1. I do not use commercial ammo, and surplus ammo is too expensive and not consistant enough for me to waste my time and money on it.