Hey Lisle,
Great question! You can absolutely install the plugin on a single subsite of your mulstisite installation and register it directly to that subsite.
If you want to control the plugin on a network level, then you will want the mutlisite license instead.
Here is a good breakdown of the difference between single and multisite licenses:
https://theeventscalendar.com/knowledgebase/multisite-license/
Does this help answer your question? Please let me know. 🙂
Cheers!
Geoff