Hi Steve!
If you have the Event > Display settings set to use one of your theme templates, then it is possible to use the widget area from the template that is selected.
If you want more control over the sidebar area, I would suggest checking out this article which shows how Jetpack’s Widget Visibility plugin can be used to help.
And, there is always the ability to override any calendar template and there’s a ton of information on that here in our Themer’s Guide.
Does this help answer your questions? Please let me know. 🙂
Cheers!
Geoff