HubPages does not share revenue, it only shares impressions. If you get 100 visits, 60 visits contain your ads and other 40 visits contain HubPages' ads.
This means, all revenues from AdSense/eBay/HP ads/Amazon during those 60 visits are yours and all in those 40 visits are for HubPages.
If you see your Google Analytics report and compare it with AdSense URL Channel reports, you will find:
(AdSense impressions) divided by (Google Analytics impressions) is nearly equal or more than 0.6.
I said nearly equal or more. This is because you may have some referrals on which your ads are also shown. Also there's no perfection in the 60% impressions rule as HubPages cannot guarantee you traffic. It is just an approximate measure, but your ads are shown at least 60 percent of the times.