If we add the Ical feed to the HCL Notes client's calendar, the data will be displayed (by overlow), but an attempt to open the event from the calendar (from overlow) has resulted in an error: Notes cannot import your file at this time. Your file is not supported.
This happens only if the external ical has the DATE-TIME value specified in another format instead of UTC time.
With the other mail client (Outlook and Gmail) it works properly. Thus Notes client should also plan to process/add Ical without UTC time.