Regulation 29CFR1910.178 (para L) Operator Training, Power Industrial Trucks, clearly and repeatedly states that it is the employers responsibility to train and evaluate each driver regardless of previous training.  All training and evaluations must be site and equipment specific.

Formal training should include lectures, videos, written testing, and practical driving skills.  Employer must certify that each driver has received the training as required by 29CFR1910.178.  Training should be conducted by an experienced trainer, who by possession of a recognized degree, certificate or who by extensive knowledge, training and experience meets the necessary education criteria.

If you have an Industrial Lift Truck in use at your facility the Occupational Safety and Health Administration (OSHA) mandates that all operators of Industrial Lift Trucks be certified.  There is a substantial fine for failing to have this certification.