Hey Andy,
That’s a great question!
Whether you run an multisite network or have two completely separate sites, the best way to share content from one site to the other is to use our iCal Importer. Install that on the the site you would like to pull content into and it will fetch the content on a scheduled basis. You could even install it on both sites if you want both sites to fetch events from each other.
Does this help answer your question? Please let me know. 🙂
Cheers!
Geoff