I would make your Dervish a mixed blood offspring from genies and humans - this would explain their superhuman abilities..
As for Arakis Freemen they were much more than pure raiders... Actually they were very technologically advanced - something like modern Iran, probably, which even has a special holyday devoted to nuclear science and technology...
To Endoperez:
Thanks, I appreciate your workings. It's just that this one position looks wrong to me. I'll probably try to make alternative one based on this if I'll have time tomorrow. It'll probably look bad but could give you an idea...