Yes, it's possible, but not easy.
WordPress multisite saves each site's data in a separate set of tables. Each site's wp_db object only knows about it's tables. There's a nifty function called switch_to_blog() that allows you to grab data from other site's tables, but it's *very* slow as everything has to be dumped and reloaded every time you switch. Plus you have to cram all the queries together, sort them to get everything in order, then display them.
The better way would probably be to hook into the save/edit/delete function(s) and have all events saved/updated (as duplicates) to a single site then use that as the data source for your combined events table. That way the heavy lifting is on the backend and not on every request. But that's no walk in the park either... and may not be completely possible without adding some hooks to the core plugin files -- I can't remember if we have hooks for all those scenarios in there yet.
If you do attempt it (or hire a dev to do so) good luck and let us know how it goes.