Usually, Second Officers are used on long haul flights, as a way of providing enough crew for the time distance without using two experienced FOs. This way, you can use someone who is new to the company. Not many airlines do this any more, but a few in Asia do.
When operating 1-3 hour hops, I can't believe they'll have a third person (in the already cramped cockpit) to take over duties, but I could be wrong. I assume it's just a way of justifying payscale...they are recruiting DE FOs so they probably start at the usual rate, but cadets will start at a lower rate, having their training paid back and on a reduced salary. Perhaps Second Officer is the 'label' for reduced salary cadets.