we have to be careful with the term 'finished' here. this, in strict guitar terminology, refers to a colour + lacquer coated application. a good example would be Gibson's neck, where the rear (where you rest your thumb) has a pigmentation & lacquer application.
the finish on maple necks (eg: Fender) is simply a relatively thin sealant which is buffed at the factory to make it feel flushed with the wood material. if this sealant is absent, your guitar neck would feel like the bark of a tree, absolutely bare to the touch. thusfar, i've come across one such neck- Yamaha's Mike Stern signature model.
i haven't come across a finished maple/ rosewood fretboard, if you do, please link us your discovery.