Hi,
I think we can add only one models record in a calendar view. But you can see in the base calendar view meetings as well as the time-off is present. What they have done here is whenever a time-off gets validated the corresponding meeting gets created. That is the time off in the calendar is actually a meeting. So you can do the same way like what they have done here. Whenever a meeting gets created a corresponding task should create in the project.task model with all the necessary values like name , start date n end date etc. By this way you can see the meetings in the field service calendar view.
Regards