React (and Om for cljs) looks extremely appealing but I imagine it is probably not possible to use non-React components e.g. jQuery and jQueryUI ones together with React code on the same page/app.
Can anyone confirm?
Yes, react can play well with your libraries.
Check out the documentation:Integrating with Other Libraries
getDOMNode(), etc that will allow you to integrate your existing jQuery plugins to work with React. See facebook.github.io/react/docs/working-with-the-browser.html for more info.