According to Discount Tire, the Unique 297 black steelie works on the Dakota. Its specs also match those of the wheels that fit the X...however, they DON'T list it as fitting the X. Maybe they just never tried it.
If you confirmed that Dakota wheels fit on the X, and they confirm that Unique steelies fit on the Dakota, it's possible that Unique steelies fit on the X. What model Dakota did those wheels you tested come from?
If there were a discount tire near me, I'd be there test fitting the Unique 297 black steelies. Has ANYONE done this?