Yes it is good to soak nuts before putting them in your smoothie. This makes the nuts much easier to digest because soaking them neutralizes the enzyme inhibiting phytates.
As for dehydrating... I have seen it recommended to dehydrate them as well but I have yet to see, or hear why. While I do suggest pre-soaking I generally don't suggest dehydrating nuts.
If anyone comes across info as to the benefit of dehydrating nuts after soaking them, please let us all in - I, for one, would love to learn more.
