Hi there Michelle,
Thanks for getting in touch with us! I can help you on this ๐
Let me start by saying that although I’m not much familiarized with ‘Ultimate Member’ plugin, the most common thing in this kind of plugins is that they work extending WordPress Users functionality. This means that most probably if you log into the site using ‘Ultimate Member’ plugin login form, they will be recognized as logged in users along the site. If this happens then the user submitting the event will be the author of said event. Does this makes sense to you?
Please let me know about it,
Best,
Nico