The Ghost is unaffected by the Confusion spell. While there is no strong statement that all creatures affected by a spell are "targets" of the spell, I did find this on page 205 of the PHB:

Many spells specify that a target can make a saving throw to avoid some or all of a spell's effects. The spell specifies the ability that the target use for the save and what happens on a success or failure.

This seems to imply that the targets of a spell are any creatures affected by it, although it's obviously not as clear as we could hope. Another example, on page 196:

If a spell or other effect deals damage to more than one target at the same time, roll the damage once for all of them. For example, when a wizard casts fireball or a cleric casts flame strike, the spell's damage is rolled once for all creatures caught in the blast.

As backup for this, we have the Ghost's Possession ability on page 147 of the Monster Manual:

The ghost can't be targeted by any attack, spell, or other effect, except ones that turn undead[...].

Turn Undead is an AOE ability, not a targeted one. If the Ghost was still meant to be affected by AOE spells and abilities, the caveat for Turn Undead would not be necessary.

And finally, if AOE spells did affect a Ghost in the midst of possessing someone, the Ghost would be affected by every Fireball or Lightning Bolt that hit the possessed creature. In your fourth point, you asserted that this obviously wasn't the case, which I agree with. There's no reason why Confusion would work differently than every other AOE spell.

No, it does not.

The Dispel Magic description says:

Choose one object, creature, or magic effect within range. Any spell of 3rd level or lower on the target ends.

And Animate Dead has a duration of:

Duration: Instantaneous

So there is no spell effect to dispel as Animate Dead has a duration of instantaneous, so as Dispel Magic only works on a spell it has nothing to work on and does nothing. Also clearly stated here stated in this Sage Advice:

Can you use dispel magic on the creations of a spell like animate dead or affect those creations with antimagic field? Whenever you wonder whether a spell’s effects can be dispelled or suspended, you need to answer one question: is the spell’s duration instantaneous? If the answer is yes, there is nothing to dispel or suspend.

The control of the undead granted by the spell is a consequence of the spell being cast, not an on-going magical spell, in the same sense as the fires started by a fireball are an on-going non-magical effect. The zombies are strictly loyal to the caster for a period of time, bonded to them like ducklings are to their mother, and in the same way the fires and damage from a fireball last for a period of time and cannot be dispelled, neither can this bond.