I believe it is of the same Norse derivation, though if I refer to:
This dictionary was composed by Ewen MacEachen, a priest from Arisaig and noted Gaelic scholar. It was first published in 1842.
Rannsachair, -ean, m. a searcher.
Rannsaich, -te, -achadh, a.v. examine, search.
Rannsaiche, -ean, m. an examiner, a searcher.
And from An Stor-data Braithrachais Gaidhlig 1993:
Rannsachair: Explorer n. masc.
Given my Orcadian/border Scot/Argyll Gael ancestry - perhaps the Irish interpretation is more apt!