StumbleUpon is a social bookmarking service, just like Digg and Reddit.
If you are looking to benefit in a commercial way, all you can do is build a popular profile and ocassionally submit one of your hubpages articles.
The rule of the internet goes like:
"You must give a lot, before you can receive."
Which in this case means - submit a lot (give) to stumbleupon, then start submitting your own content from time to time (receive) in order to drive traffic to your articles.
As a rough estimate, assuming you build a profile with about 1500 submissions of fresh, interesting content on a topic that drives you, resulting in about 60-110 subscribers, stumbleupon will drive traffic of at least 300 visitors for a day. Usually, after submission, traffic lasts for 2 or 3 days, 4 tops.
Of course, that is if your post does not succeseed on going viral. Then the results will be more than great.
So, in a nutshell, you can make money WITH stumbleupon, but not on the site itself.
p.s. If you are uncertain which one of the Hubpages' options for article monetization are the best for you, then you can see my hub: Hubpages VS Adsense - https://hubpages.com/business/What-earns-you-more-...
p.p.s. I'll be publishing a hub, in near feature, about building a profile on a site like stumbleupon. So, just as an additional idea - you are invited to subscribe.