ISIS themselves have said they're sending insurgents via the refugee streams. It's a strategically intuitive thing to do. They aren't going to abstain from doing that on some fair play scruple as has been amply witnessed on numerous occasions.
I don't personally think Ireland will be a priority target. I suspect Ireland is being used as logistical conduit for Saud and Qatari funny money -- at least for AQ "moderate rebels" and if Ireland is a hub for that kind of carry on, they won't want to draw undue attention to themselves by bombing here.