I think you may not quite understand how soul skills work. Before a game begins you choose 5 cards to put into your soul card section, they each have their own lp values and lose them in order. One of the causes of losing lp is a card being buried. In your example it sounds like your dryad died and you expected its soul skill to go off, but what happened was its death depleted the last lp of one of your soul cards and that soul card's soul skill gave +attack. Because you thought soul skills were based on units, not the seperate soul cards, you assumed it was the dryads effect that had gone off. However Soul Skills do absolutely nothing unless the cards is in your soul cards, so if a dryad is played as a unit you can ignore its soul skill as it will never come into play.
If I'm misunderstanding you, my apologies, just offering up a possible explanation as I have found the dryad soul skill to always boost defense exactly as its supposed to.
The bunnies of Lavato have special abilities, like 'Action Skill: Make Carrot Disappear.'