In the event that you spray finish onto a maple neck, you normally do not have to tape the frets. However, it depends on what exactly you are doing.
When I did a recent strat, I had this question and my luthier said that we have to do a fret level and polish anyway which removes the lacquer/ varnish off the frets.
Even if you are varnishing a neck that you know does not need any leveling , it would still be faster and more practical to finish over the frets and clean them up later than to try to perfectly tape off each fret.
As already mentioned, rosewood,ebony and pao ferro boards don't need to be finished.