Third party Certified hot water tanks

So I know there is a lot of things wrong with this water heater. But my questions comes to the third party certified part on hot water heaters. Is there different ways that they leave certifications? Do they tag it? I asked a professional plumber about this and he said they don’t need to be certified, but after looking up the code I know they do. Also the gas line in the picture, can it be a flexible hose connected directly to it like shown as long as the hose still has a shut off valve feeding the tank?