Does Dervish Dance say "wield" or "carry"?
Archives of Nethys has: "You cannot use this feat if you are carrying a weapon or shield in your off hand."
That may very well be different than wielding, but I don't have the book in front of me.
It looks like one of those "fine distinction" differences, such as wielding a two-handed weapon one-handed vs wielding a two-handed weapon "in one hand". Wielding a weapon in your off-hand includes both "virtual" wielding as with Spell Combat where the spell virtually counts as an off-hand weapon being wielded as well as weapons not hand-associated such as armor spikes or boot blades or non-punch unarmed strikes. By contrast, "carried" means held in your actual hand so Dervish Dance could very well be used in conjunction with non-hand-associated weapons as well as weapons that aren't "carried" such as a spell being cast by Spell Combat or a Punch.