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That's an interesting question. The compound eyes may or may not be functional, but if the larva is not using the information from them, then it's not really using them at all. We know that the larvae of several species of Chaoborus feed at night, and my understanding is that they rely on detecting water movement, rather than vision, to find their prey and avoid being eaten by others. Vision (using their simple eyes) is used to assess light levels and determine whether it's time to go up or down in the water column.
It may be that other larvae with less transparent cuticles also have developing compound eyes within them, but as we can't see them, we assume they're not there.