How can create an objective to find hidden props and destroy them?

You should be able to use the Stat to Track - Events option on the Tracker.

You will need to use prop manipulators, but only small ones, one on each vase.

Then in your Tracker,
Stat to Track set as Events
set the Target Value to 4 for the 4 vases

and in the User Options - Functions,
use the Increment Progress and add 4 Array Elements
Eye Dropper the 4 Prop Manipulators onto the Array and set them to On Destroyed

Everything else you can set to your preference.

Hopefully it does what you need.