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Diesel engines for power generation will have a governor control that sets the throttle based on the load to maintain whatever rpm is required for 60 Hz (constant speed control). The load in this scenario is uncontrolled and the genset simply follows it.

A diesel locomotive's engine controls are about producing the right amount of power to match the operator's throttle control. Electrical frequency at the generator (alternator) terminals is irrelevant since that output is being rectified to DC anyways. This is great for a train, because it means you can have full power at any speed - the speed of your train and the speed of your engine are completely decoupled from each other. But if you now connect this normally variable frequency AC output directly to 60 Hz loads, you will need to figure out how to set the throttle to best maintain something close to 60 Hz and your power output will be limited.