You can see who viewed your live event within your Event Check-In tab in the manager portal whether your event has tickets or not.
Anyone with the green checkmark and Checked In next to their ticket logged in and viewed the event. If you see a circle and Check-In with a blue background, that means they did not log on to view the event with that profile.
If someone without a ticket associated with their profile views your event, you will see their name appear in the EventCheck-In tab with a ticket titled 'Registration'. They will show a green check-mark and Checked-In showing that they viewed your event.