In ours, the iframe has been for viewing only. Unless there's another version out there for embedding, I think you've got to enter all events in google.
Google calendar has a lot of amazing functionality, and for viewing events it's a great complement to a wiki. It's possible to open event windows from within the iframe — but that window varies for users with/without google logons. Non-googlers get a dumbed-down event summary, so I usually include this html that links to event info elsewhere.
<a rel=nofollow href="URL" class=linkified target=_blank>TEXT</a>
For anyone who wants to write to the calendar, it's another layer and not very much like a wiki. You can parcel out write-access to different users. Or I suppose you could set up a generic google logon and share that around.
The main disconnect is in tracking calendar changes. You can set up an RSS feed to track new events. But I haven't figured out a way to track event changes or deletions. And if someone deletes, there's no option for reverting.