Hi,
Thanks for the interest in our plugins.
I can help answer your questions.
We do not guarantee compatibility with any theme except the WordPress codex themes of Twenty Sixteen, etc… It is likely it would work, but we cannot say for sure.
You can try your theme with the core version of the Events Calendar found for free on WordPress.org: https://wordpress.org/plugins/the-events-calendar/ If it works there it will work for Pro as Pro is an Add On for that plugin.
If the above is possible, my next question would be whether there is a compatibility with Gravity forms so that an event organizer can fill in a form which then pre-populates the fields to add a new event to The Events Calendar plugin.
Unfortunately, we do not have any features to connect to Gravity Forms to do this. It is possible a form could be created to do this as the events are custom post types and use custom fields, but that is beyond the support we can provide to help out on a customization such as this.
We do have the Community Events Plugin that does enable front end event submission:
https://theeventscalendar.com/product/wordpress-community-events/
That is a separate plugin from Pro, but does not require Pro to work on the free version of the Events Calendar is needed.
Let me know if you have any follow up questions.
Thanks