More specifically an EE rating means spark enclosed. Meaning that any electrical component that creates a spark is enclosed, such as the motors and contactors.
An EX rating designates that the machine is spark proof. An EX truck is not only spark enclosed but also any part of the forklift truck CAN NOT create a spark. The chassis of the truck has a bronze band around it so that if it were to rub against steel there would not be any spark created. The forks are bronze as well and all the wiring is protected in conduit.
The add on price for an EE rated truck is relatively small- probably around $1500 where as only specialty manufacturers make EX trucks and they carry a hefty price tag. If a standard 5000# sit down electric were priced at $30,000.00 a similarly spec'ed EX version would probably be around $80,000.
As far as who would tell you which you would need, EE or EX, as far as I know your insurance carrier is the only one that has that authority.