I wrote an email to the team at hubpages and asked this question::
1. If I create an ebook or app out of a hub article, do I have to remove it from hubpages?
They answered my question (and probably yours) by simply replying: "You are free to publish your work elsewhere after first publishing on HubPages."
That's the answer I received which I'm using as a guide for myself. You can always ask for more clarification by contacting the team at hubpages. This address is a bit difficult to find, but it's on this site somewhere :)
I finally realized, however, that if I create an ebook for sale, anyone who bought my ebook would be upset to see it for free. Ebooks are not easy to sell without lots and lots of promotion.
Even though I received the answer above, when I publish on bubblews, I simply write a summary or introduction to my article on hubpages and then link back here. That way I feel very safe. I probably don't get as many "reads" that way, but bubblews is so "easy" with the money that you don't need that many views to see a few shekles trickling in.