Q. Can students see an announcement from a non-published course?

No.

Not until the course is published.  Announcements will not be emailed to students and they will not be able to view them in Canvas.  If you want to communicate to students before the course is published, use the Course Emailer tool instead. If an announcement was created in an unpublished course, a notification will not be sent to the students retroactively if the course is later published.