"Liken" doesn't strike my ear as being particularly strange. I'm sure I've used it in formal writing before, probably more than once. "Liken unto", however, is something that it would never even occur to me to use. The word "unto" strikes my ear as a very forced mannerism, and if I hear it spoken it trips my give-me-a-break-ometer. If I came across it in, say, modern academic writing I'd probably laugh aloud, honestly.