Interesting Tom. I hadn't heard of Kerr as a Welsh name. In fact, there's no letter 'K' in the Welsh alphabet. After reading
this article, I'm wondering if it was morph'd into Scotland from a different original (Welsh) spelling, e.g. "Cer" in Welsh would be pronounced with a 'hard c', and sound like the English 'Kerr'. Conjecture and some creative thought on my part.
OTOH I know that many Welsh names were misspelled at Ellis Island or on the ship; Folks wrote down what they heard, not necessarily the 'correct' name.