Debated. The mound is a real tomb. The page does not treat the high kings as a settled fact.
The Mound of the Hostages stands on the Hill of Tara, in County Meath, Ireland, near the River Boyne. It is a passage tomb about 5,000 years old, the oldest monument on the hill. The mound is about 15 metres across. A side entrance leads into a passage about 4 metres long, with old carvings. Archaeologists found cremated bones and grave goods from the Neolithic period and the Bronze Age. In one dig, they found the remains of a young person from about 1350 BC, with a necklace of beads thought to come from Egypt.
The page says the question of whether those beads came from Egypt is still little studied.