Can he look at the center cards?

No, only other players’ cards, one at a time.

How do I unlock the Ghost Hunter?

He is part of the Shadow Pack, available in the game’s shop with Moons.

Team: Village

He investigates the shadows… and may become one of them.

Power: Looks at up to two cards. Finds a wolf or the Tanner? Joins that team.
At night: Wakes up in position 7
Win condition: At least one werewolf is eliminated… unless you joined the wolves or the Tanner.

The Ghost Hunter wakes up after the Seer. He may look at one player’s card, then possibly at a second one.

If he finds a wolf or the Tanner, he stops immediately and joins that team: he becomes a wolf or a Tanner. Otherwise, he stays with the village.

As with the Doppelganger, the transformation follows the card: if it is later stolen or swapped, its new owner inherits the team.

Looking at a single card is safer; the second gives more information but may make you switch teams.
Once a wolf, you know at least one of your partners: cover each other discreetly.
Once a Tanner, your only goal is now to get eliminated!
Looking at a single card is safer: the second one may make you switch teams.

Can he look at the center cards?: No, only other players’ cards, one at a time.
How do I unlock the Ghost Hunter?: He is part of the Shadow Pack, available in the game’s shop with Moons.

Create a free game and invite your friends: the game does the rest.