According to the universal monster rules, incorporeal creatures (read: ghosts) have no Strength score:
[An incorporeal creature] has no Strength score, so its Dexterity modifier applies to its melee attacks, ranged attacks, and CMB.
The ghost touch special ability allows a piece of armor to both function properly when being struck by an incorporeal creature, and to be "picked up, moved, and worn by corporeal and incorporeal creatures alike."
However, armor still has weight, and all incorporeal creatures have an encumbrance limit of 0 due to their lack of a Strength score.
Does this mean that it's actually impossible for a ghost to wear ghost touch armor even if it's technically able put it on?