It may be 1% of total housing stock but what is it relative to long term rental stock? It wouldn't take much to have a significant effect on the cost of long term rentals.
Google says that 30% of the population is renting in Ireland, I imagine that it's a bit higher in Dublin... but yeah. I think it's reasonable to say there's an effect.
I don't think that it is the primary effect, but we can walk and chew bubblegum!