Not fully - but we have used it in a few different ways.

• Some groups who are inviting their Igloo calendar to their existing Outlook events using the custom calendar email address functionality. But this isn't really for functionality, it is more for added event visibility on Igloo while users already also have it on their Outlook calendar. The flaw is that the invite has to come from an individual with an Igloo account - not a group email address - i.e. "communications" - otherwise we'd probably use this functionality more. 
• We use it for scheduling out in advance firm events we know will not change and don't need to be on everyone's calendar - i.e. firm holidays. 
• We also recently used the Igloo calendar for a large event series we were hosting, and while the RSVP function is clean and easy, and auto populates a calendar invite with all the event details to the attendees Outlook calendars, there is no functionality to contact those who have RSVP'd. If the date/time change, they can be notified through Igloo, but if you are just changing a detail within the event - for example, adding a Zoom link or other details, they don't get notified and their Outlook calendars don't get updated.

Thanks Molly! We're using it in very similar ways so this is very validating.  Still wondering if anyone has gone beyond this and is using it more seamlessly for small team calendaring.