Merging IOS calendar data to 3rd party calendar

[rmm1]

There are some great 3rd party calendar apps but sadly their features require you to use their own calendars (Saisuke for example).

Is there a way to merge the IOS calendar with the SAISUKE calendar. I know everyone talks about Google calendar but I travel a lot and some of my locations just don;t have Internet so the google option is not for me.