Spiritually, hearing clearly suggests being able to understand what is being said or conveyed to us.
To be able to hear is somewhat different to listening, which suggests assimilating information at the same time.x100
Psychological / emotional perspective: Sound suggests a particular vibration is created and hearing that we have responded to that vibration. In dreams this can occur on a psychic level when we are conscious on waking that our perception has altered.
Material aspects: In practical terms a hearing in a legal sense suggests that we will be listened to and understood. Not to be able to hear in dreams suggests an unwillingness to listen, whereas someone not hearing us suggests that we need to alter the way we are communicating.