Just like the title says...does making a ranged attack exhaust the unit making the ranged attack, or can that unit attack in the subsequent combat phase?

My understanding is it only changes when the unit attacks. So it exhausts to attack in the ranged phase and then is unable to attack in the normal combat phase (unless it has a way to ready itself like Nadregs Flash gits)

Yes, you have to exhaust the Ranged unit when it attacks during the Ranged Skirmish. Ranged attacks are just like any other normal attack - only the timing changes (they get to go first).

Note that the Ranged Skirmish is not a separate combat round. It is part of the first combat round in the battle at that planet. So in the first combat round at a planet, players take turns attacking with their Ranged units, then take turns attacking with their normal units. Then, assuming no one has won the battle, all of the units ready and players take turns attacking with all their units. It is the fact that Ranged is not a separate combat round or phase that confirms that the units must exhaust when making a ranged attack.

Yeah, in the first round only Ranged units all basically get to shoot before ANY other attacks are made - if there is a single Ranged unit left Ready (on either side) then players alternate taking shots (attacking) until no-one has any ranged units left Ready. That means if you brought enough (and the only guns) to the fight, you could potentially get to blast away with all of them without retaliation.

However, if anyone is left alive after all the Ranged units attack, then the non-Ranged also attack. If anyone is left alive STILL, then everyone readies and a new round begins, but Ranged no longer have priority.

The moral of the story is...need more guns! LOL!