iOS sdk v4.0 - is userIdentifier sent with lifecycle events



How is the userIdentifier used within the iOS sdk v4.0  is this stored and sent back with lifecycle events?  We want to match lifecycle events to users of the app.

The use scenario I envisage is that we would be able to implement a processing rule to pick up the userIdentifier and assign it to an eVar, and we could then pull reports for lifecycle events against userIdentifiers(eVar). 

Is this possible?