The default Event Calendar’s query will ask only for ‘event’ post type.
You need to hook into pre_get_posts WordPress action, filter proper query and add ‘post’ post type to query params. This is the “WordPress way” of doing it.
However, you can try doing it the “Events Calendar way”, by searching the codebase for a proper hook (I wasn’t able to find them in the documentation). For example, a quick look gave me this:
tribe_post_types filter
You can try if it works or try searching through the codebase for do_action and apply_filter calls to find a better hook.