Your Notes client can subscribe to an iCalendar feed, as long as that feed is Public. Share your iCloud calendar to Public, and iCloud will show you a URL that you can email to someone... copy that URL, change the prototol to https://, then go to Notes, Calendar, Show Calendars, Add a Calendar, iCalendar Feed, and use that URL. It's not a two-way sync, it simply adds the iCloud calendar to the same view as your Notes calendar. This works great for me to be able to see household events on the same glass as work events, without posting business data outside my company's servers.
Unfortunately I haven't been able to get this working without making the iCloud calendar public. If anyone has this working without giving the whole world the ability to stalk the iCloud calendar, please let me know.