If it has just one level of hidden volume, that throws plausible deniability out the window. If the intimidators don't find what they're looking for in the outer volume, they'll probably believe you have a hidden volume. So in addition to decrypting the outer volume, you'll have to show them the hidden volume or they'll throw you in jail or whatever their threatening tactic is.
But if it allows arbitrary levels of nesting the hidden volumes, you could decrypt the outer volume and n levels of hidden volumes, while keeping your sensitive data at level
n+1 or deeper.