There's a media report here:
Black boxes found and investigation into Cork air tragedy starts - Traffic and Transport - iomtoday
Cork Airport has a precision instrument landing system that enables safe landing in reduced visilibility due to fog, rain or snow where the ‘runway visual range’ is not less than 300 metres.
This is a category 2 ILS whereas Ronaldsway has a catagory 1 system that enables safe landing in runway visual range of not less than 550 metres.
In each case, a suitably-equipped aircraft and appropriately qualified crew are required
Which suggests Cat 2 was ok