Is it true that Weapon Finesse allows you to use your DEX bonus instead of your STR bonus for any combat maneuver that happens "in place of a melee attack" (ie, Disarm, Sunder, Trip?)
No, Weapon finesse does not say that anywhere, there is a feat called Agile maneuvers that let you use your Dex mod for combat maneuvers.
When you attempt to perform a combat maneuver,
make an attack roll and add your CMB in place of your
normal attack bonus. Add any bonuses you currently have
on attack rolls due to spells, feats, and other effects. These
bonuses must be applicable to the weapon or attack used to
perform the maneuver.
Then you have this little piece of information under the CMB description which 'seems' to say you do not need Agile Manoevers to get your dex bonus to count.