How can I trigger a matinee cutscene after a specific event has occurred.

Sure, just like this

Have a BP dispatch an event by calling it’s event dispatcher

And then have the level BP hold a reference to the BP and add an event listener on that specific event. Just need to hook it once so Begin Play is a nice place to do this. After that every time you trigger the event in your BP it’ll trigger the event in your level BP

http://s27.postimg.org/cbc51cl3n/Level_BPListen_Event.png