The Roma and Irish Traveller are different groups of people. The word "Gypsy" is really confusing the issue. The Irish Traveller have had a few genetic studies done on them and they are just a subset of the Irish. They have drifted a bit due to endogamy.
This is a bit difficult to see but it is from the Irish DNA Atlas which hasn't been released yet.
https://s-media-cache-ak0.pinimg.com...ef142873cc.jpg
They are thought to have diverged from the general Irish population about the 1300s.