I don't about Jekyll, but his website says "is a blog-aware, static site generator in Ruby", and I don't think that's the case.
A solution is to store the pages created by the users to the Database, you can use Textile and/or RedCloth (instead of pure HTML).
There is a nice railscast how to create semi-static pages, I am sure you can get some good ideas: http://railscasts.com/episodes/117-semi-static-pages
I hope this help you.