Hi
Mark,
I haven't heard of Dolfinnr, but it seems to be a variant form of the Old Norse name Dolgfinnr / Dólgfinnr.
Probably the origin of this name is the name of the creature, but later it had been changed so its meaning became 'dólgr' = enemy + 'finnr' =
Finn (originally, the early non-Aryan inhabitants of Norway and Sweden were called that; they are not identical with the modern Sámi people or Finns).
Regards,
Satu