Unlike England, the Vikings in Ireland were never present in such numbers as to effectively colonize and conquer large swaths of the country. Instead, they built coastal settlements and focused on raiding and trading. From these bases in the late ninth century, the Vikings formed alliances and fought alongside one Irish kingdom against another. These alliances shifted but could be strengthened through inter-marriage. Most famously, in 999 AD the Irish High King Brian Boru was married to Gormflaith, an Irish princess who was the mother of Sigtrygg Silkbeard, the Norse king of Dublin, from her previous marriage to Olaf. Sigtrygg was then married to Slaine, one of Brian's daughters. These Hiberno-Norse (or alternately, Norse Gaels) faded from significance after the Battle of Clontarf in 1014, though Sigtrygg held on to Dublin until 1036.
For SAGA, the Norse Gael faction is a mix of the Vikings and the Irish, leaning a bit towards the Irish. The Norse-Gaels are fairly "shooty." The Levy and the Warriors are both javelin throwers. Alternately, warriors and hearthguard can be armed with Dane Axes. They cannot be mounted as the Irish can, but on the whole, their defensive values are a bit better. Furthermore, their "gimmick" is the Challenge, in which significant combat bonuses can be achieved - if luck is on your side.
From some of my many unassembled Wargames Factory sprues, I threw together a few dedicated Norse-Gaels. The first unit of warriors below is kit-bashed from several sets to achieve a mixed Viking-Irish look.
Norse-Gael Warriors with double-handed axes below. The unit leader in front does not have a double handed axe, he has an axe in each hand. He was inspired by Floki from History Channel's Vikings - which is perhaps the only thing left worth watching on that channel.
A six point Norse Gael warband below. If all goes well, this will be my army at my next tournament.