Using Subscribe2 should be possible as it's designed to work with other custom post types.
I did have a go, but it fell over with an error.
MattyRob - the Subscribe2 author posted (http://wordpress.org/support/topic/plugin-subscribe2-notifications-for-customer-events?replies=16_
I've had a dig in the event plugin code, this is a thrown error code in one of the files.
It seems to be saying that the event details are null.
Now this might be because they are not collected at the time the filter code is called or perhaps they are nit yet created when the filter code is called. I'm not sure. I think it may be better to follow up with the event calendar author as they know their code better.