It’s odd to call Travelers “indigenous” because they don’t predate the settlement of Ireland by the current majority group. They’re Irish people who culturally diverged around 1600. It’s like calling Appalachian Americans Indigenous.
I don't think the semantics of the word indigenous are the important thing here, although I will say that officially, according to the Irish government, Irish travellers are an indigenous minority and attempts to discredit this are usually a thinly disguised attempt to discredit the credibility of the Irish travellers as a distinct ethnic minority - or, to put it another way, it's one of the more common ways that Irish people are racist towards travellers.
Instead, it's the racism and discrimination against an ethnic minority that we should focus on.
Calling them “indigenous” is a tactic to give greater moral weight to their political positions. While those positions may be meritorious, that doesn’t justify false characterizations in their service. Irish Travelers are ethnically no different than other Irish, nor does their presence in the country predate that of other Irish.
We do have our own indigenous minority who are treated badly by society - Irish travellers. There's a lot of racism in Irish society towards them, and we could do with looking at how other countries treat minorities, indigenous or not, and recognize for all that we like to harp on about our own poor treatment in history, we are doing exactly the same here towards travellers.