For a small, unplanted tank, I don't think that a drainage layer is necessary, but I also don't see what it would hurt. I wouldn't intentionally store water in the drainage layer though; it defeats the purpose of having a drainage layer.
The eco earth does not need to be bone dry. Toads appreciate some moisture. I would leave one end dry, and mist one end, giving the toad options. The leaf litter will help retain moisture.