Unarmed attacks are treated light weapons, weapon finesse applies to light weapons, so weapon finesse applies to maneuvers made with unarmed attacks.
Note that some maneuvers, like grapple and bull rush are not maxe with weapons, so even though you might logically be using your unarmed attacks to put a guy in a headlock, or what not, if it is not a weaponable maneuver, finesse is no help.
If you have weapon finesse and use a finesse weapon to make a trip or disarm attack, you can use Dex, even if you don't have Agile Maneuvers.
Can a monk, or other character with Improved Unarmed strike, with weapon finesse use Dex when tripping or disarming with a fist/foot?
Unarmed attacks are treated light weapons, weapon finesse applies to light weapons, so weapon finesse applies to maneuvers made with unarmed attacks.
Note that some maneuvers, like grapple and bull rush are not maxe with weapons, so even though you might logically be using your unarmed attacks to put a guy in a headlock, or what not, if it is not a weaponable maneuver, finesse is no help.
However, there is at least one weapon that can be used in a grapple. The Dan Bong is a light weapon that adds +2 to grapple. Of course, having one in your hand may mean you take a -4 to grapple as well, but no one is sure if that is supposed to happen or not. It seems most believe the +2 replaces the -4 rather than modifies it to a -2.
YMMV.