Ranika,

some of those Gaelic speaking islands off the west of Ireland were settled by Cromwells soldiers.

All of the languages you mentioned as influences on Welsh have been influences on Gaelic too (as well as Scandinavian and Welsh influences on Gaelic).

However, I doubt that either language could be described as uninfluenced by other languages (I don't like the term corrupted as outside influences show up in all but the most isolated linguistic communities and tend to go both ways).