[Special Coupe Frank]

If the belt is riding equally "lower" in the groove of both pulleys, then there should be no change in fan / pump speed. The effective diameters of both pulleys relative to each other is still the same.

If the belt is touching only on the inside, flat surface of the belt, and not the Vee sides, it might slip on the generator pulley, and if you have to crank the belt tension up to prevent slippage, that could cause accelerated wear on the water pump and generator bearings.

Then again, it might be fine.