There are 2 types of inspections for SCUBA tanks. The one you mentioned is done every year and it tests for pressure integrity. The other which is done every 5 years is an internal inspection of the tank and it is usually sent out somewhere and a special scope is used to check the inside of the tank.

Once a tank is designated as SCUBA is not supposed to be used for anything else. The shop can get into alot of trouble if they were to fill it without it being approved for safety.