In adventure mod its not possible to use a hoe on grass or dirt. it doesnt matter if the tool has the CanDestroy:[grass,dirt] tag or not. Maybe a additional tag (something like "CanUse:[]") should be added
EDIT: picking up water with a bucket or a bottle doesnt work too
This works as intended. In order to till grass/dirt, use the "{CanPlaceOn:[dirt,grass]}"