There should be a distinct audio cue for spawning enemies and, if possible, some kind of audio cue to let you know where they are on the map (i.e. a distinct walkie talkie squelch, or some kind of Destiny or Metal Gear patrol-like chatter between enemies)
When an ally is knocked out of the fight, there should be an audio cue (i.e. "Freelancer/Javelin Down") so you know to go repair them.
Most of this is fixed in the mix. Maybe we will add a bigger UX sound to teammate down, that is good feedback.