Unfortunately Pages does not fully support the epub 3 standard in that they don’t support the embedding of any .html file types in books..
This might be something coming soon since it is a feature in iBooks Author that they can port over. Until that time, I recommend working with regular iBooks Author if you have Hype documents you want to place in epubs or with Indesign.
I recommend sending feedback to Apple and requesting that they allow embedding wdgt or HTML iframes within Pages: https://www.apple.com/feedback/pages.html
The production of interactive textbooks was a huge initiative by Apple (under Stave Jobs) and I would love to see them continue to improve their tools.