You can add guests to a recurring event as long as you add the guest to the first event in that series (i.e. the ‘master’ event)
Steps
Select My Apps in the top menu
Select Events
You arrive on the Manage Events page
Press the Filter filter
The Filter Overlay loads
In the Type section, make sure the Master checkbox is ticked
Press the Apply button
The table updates. Press Close to close the Filter.
Click through the page numbers until you find the event you are looking for
Select the title of the event
You arrive on the event page
Click the Add Guests button
The Add Guests popup loads
Select the contact(s) you want to add to the event.
Select Update this and all future events if you want that contact to be added to all the events in the recurring event series.
If you add guests to a subsequent event and click Update this event and all future events the guest gets added to all the subsequent events.
Adding a guest to an event, now you can see that the guest is also added to the future subsequent event.
The popup closes and the guest(s) are added