I doubt any smog tech would actually spy and check to make sure the cat is carb approved (a state smog referee would), but the problem is that 99% of places will not ship or sell to a California resident if the item is not CARB approved.
The old style jerry cans for instance are not CARB approved. Only way you can get one is get it old or one without a spout, because the spout is the problem. I have one newer ATV style jerry can that I had to buy the spout and the tank separate just to get around the dumb rules. There's no way around a cat that I know of though (outside of drop shipping to someone to have it re-shipped.)