Hi Katherine,
Thanks so much for your interest in our plugins! While The Events Calendar and Event Tickets Plus certainly work great together, you don’t need our calendar in order to make use of our ticketing features. Once Event Tickets and Event Tickets Plus have been installed on your site, you’ll be able to add tickets to any post, page, or custom post type of your choice, just as you would add them to a calendar event. (And should you choose to add The Events Calendar later, it’s a quick installation and won’t change any of your existing settings.)
Does that help to answer your question? Let me know if you should have any others or if I can clarify anything else for you! 🙂 Thanks again for stopping by!