No, attendees either need to purchase a ticket level (not an add-on) or be a guest of someone who did purchase tickets. You can sell tickets using the mobile app or you can manually enter a new attendee using the event page URL.
If they are a guest of someone who did purchase tickets, you just need to update the attendee information using the edit icon on the Event Attendance grid. See this article for an example: https://support.associationsphere.com/en/support/solutions/articles/67000732516-what-if-the-ticket-purchaser-doesn’t-know-the-names-of-all-their-guests-when-they-buy-the-tickets-