UK Foreign Office advice. Now some might disagree with that assessment, but for UK citizens, it carries legal weight. Ie travel insurance will not be valid in those areas where travel is advised against. Consult your own country's foreign ministry for advice.
Aer lingus and Ryan Air only allow service animals in the cabin. This is irish government regulation. I assume you already know rabies requirements for UK and Ireland and how the common land border has impacted animsl movement regulations.