No, the Dryad does not work on stoneheart units.  They have their own special jobs to do supporting your army.

I did test this.  I selected a random castle on the map and picked some stoneheart units to send as reinforcement.  I selected and then deselected the Dryad and the numbers did not change.

I tried this again with Undead Dragons and selected and deselected the Dryad, and the defense total at the bottom right did change.

thank you for the response, have a wonderful day.

Hello Lord Pokie , has right Tina Klaus , that champion give the defense bonus just to the normal units.

You can easy test that selecting normal units with and without champion for send reinforces to a castle  and after that test in the same way with stoneheart units !

I wish you a great day and enjoy the game !