Quoting Dave Morris on this subject:
"...You've bought the Dragon Warriors books, so your Legend is entirely up to you. We don't have no truck with authorial privilege in these parts. But I do have a good reason for recommending that you don't start neatly indexing elves and dwarves and what-have-you into suitable player-character templates. That's because it will ruin your game.
Mike Polling (the author of "The Key of Tirandor", an excellent scenario in White Dwarf #49-50 that is to be reprinted in "In From The Cold") describes a problem in fantasy fiction and gaming that he calls taxonomic reduction. It begins with a demand for details about elves, for example - their social organization, clothing, breeding habits, and so on. So you get a supplement with all that stuff... hit points for Grey Elves, magic for High Elves, eye colour and what they eat. Now you can play an elf. But actually all you are playing is another kind of human being.
Okay, so now your players start to sense that something has gone. Elves used to be mysterious. Now they know more about them than they do about Yanomami Indians. So you have to bring in something new. You scour legends until you find Trows, say, or Sith. Just words. Now they take the place of the elves who have been filed and categorized into meaninglessness. Yet pretty soon a player says, "How can I get to play a trow character?" and the whole reductive process begins again.
The point is: you don’t need player-character elves or dwarves. Unless of course you want to recreate Lord of the Rings in your games, in which case stop playing Legend right now because it’s not that kind of setting - what you want is D&D or MERP. Human beings (or rather mortals, as the term is in Legend) already have infinite diversity. If you aren't able to find that in your own role-playing ability, dressing up as an elf isn’t going to do it for you.
We have to have the rules in role-playing, but they’re a necessary evil. They shouldn't be allowed to shape the way we think about the world and characters. And most especially they shouldn't be allowed to stifle the magic and mystery that's the whole point of choosing Legend as your game world in the first place.
Of course, DW is a game system as well as a milieu. So you're perfectly at liberty to chuck out the low-magic medieval setting and spooky flavour and just use the rules for combat and magic. My own gaming group did it the other way round: our games are set in Legend but we use our own GURPS variant, 7URPS."
(Posted 24 August 2010 in "Fabled Lands")
If you want to create DW professions for non-humans, then that's fine. Personally, I prefer Dave Morris' approach and limit my players to humans only... That way the non-humans remain strange and exotic. (But that's just my preference.)