As others have pointed out the copyright is yours and the duplicate content rule applies only to content published and publically available online.
However, if you were going to sell the same content in an ebook that someone could otherwise read for free by visiting hubpages, then you would need to think of the ethical and professional implications.
What I mean is, you could get a very poor reputation making some folk pay for what they could (had you told them) get without paying!
So, yes, go ahead but I would strongly advise that you remove from hubpages those hubs which you wish to sell in your ebook, first.
Otherwise, you could end up shooting yourself in the foot, as they say.