I have travelled to Ireland.
Many a time and oft.
With my dairy allergic son.

As with all airlines the more fuss you make BEFOREHAND re the flights the
more seriously they'll take you.

As for Ireland itself - it really depends on where you are. Ireland is a very
dairy rich country and a lot of foods have dairy in them. It is one of the
lowest users of corn in the world - we don't grow corn usually and don't use
it in our foods. In the more rural areas you'll just have to be careful.
People are generally friendly and very accommodating. But you'll just have to
explain in detail what you want.

People in Ireland are neither more nor less aware of allergies than the world
in general.

Have fun! And bring your rain gear!