The entry I am familiar with is from 3.xE.
Dervish – Class – D&D Tools
In fact, it was a prestige class in the Complete Warrior I believe?
There were no religious ties at all on the class. So I disagree that it would be a zealot barbarian at all. Nothing about that subclass evokes the similar feel, having played both. And again, there was not implications that a Dervish in 3.x had to be religious at all.
I would also not characterize the movement as simply spinning. I would say it was like the blade dance/song from other classes or prestige classes. A performance or action you could only do so many times a day, for only so long as allowed. Governed by a number I cannot recall immediately. It as well required movement between each attack. It allowed you to use your full attack while still being able to move about. There were other perks as well.
Likely a more desert feel with scimitars and other real world connections to the word Dervish.
I suppose I just like the image and thought of a character flitting or dancing about some opponents, whether that be skillful flurries of the blade against one. Or graceful but deadly movement through a group.