No. All tags are converted to unicode when they're read from the files, so as far as the rest of rockbox is concerned, all metadata is in unicode. Virtually everything in Rockbox deals only with unicode text.
I assume you want this because you don't like how unifont looks, and you want to use a nicer looking font when possible?
The fix there would be to find a better unicode font (or make one) and contribute it to our font collection