Yes, a ghost can take these feats, assuming its Strength is high enough, because a ghost has a Strength score.
Same as the base creature, except that the ghost has no Constitution score, and its Charisma score increases by +4.
(Ghost Template Description)
Nothing here says that the ghost loses its Strength score. They lose any Constitution score, but not Strength. The ghost’s Strength is “Same as the base creature.”
Moreover, the ghost even uses its Strength score:
Corrupting Touch (Su)
A ghost that hits a living target with its incorporeal touch attack deals 1d6 points of damage. Against ethereal opponents, it adds its Strength modifier to attack and damage rolls. Against nonethereal opponents, it adds its Dexterity modifier to attack rolls only.
Draining Touch (Su)
A ghost that hits a living target with its incorporeal touch attack drains 1d4 points from any one ability score it selects. On each such successful attack, the ghost heals 5 points of damage to itself. Against ethereal opponents, it adds its Strength modifier to attack rolls only. Against nonethereal opponents, it adds its Dexterity modifier to attack rolls only.
(Ghost Template Description, emphasis mine)
These explicitly indicate that a ghost has a Strength modifier to use. They don’t get to use it against non-ethereal opponents, but it still exists, and that’s good enough for Power Attack and other feats.
While manifested, the ghost does lose their Strength score—but this is just temporary. In theory, one could argue that if the ghost “leveled up” while manifested, they wouldn’t have the Strength score necessary to take the feat, but since it is not their default state, and ghosts are almost-always NPCs that don’t level-up anyway, this can be ignored.
Beyond that, the game supports meeting prerequisites with temporary effects. The game isn’t really clear about how exactly that works—it’s a concept that’s alluded to but never really explained—but the general consensus is that it’s fine to allow characters to meet feat prerequisites with temporary effects—after all, the game covers what to do if feat prerequisites are lost, you just can’t use the feat. So if you meet a feat’s requirements temporarily and then no longer meet them, you just can’t use the feat. Most DMs will allow this kind of thing even if the source of temporary access to a prerequisite isn’t necessarily active at the moment of leveling up (for feats; prestige classes are a different story because once you take 1st level, prerequisites no longer matter, which can make temporarily meeting the requirements rather cheesy and something DMs may want to stop).