The brackets should work fine fastened to the side of the Fantastic fan, but I've never seen them installed with sheet metal screws. The housing is plastic. I'm not sure a sheet metal screw will stay tight in the plastic.
They come with machine screw, washers, and nuts. They are suppose to drill a hole and use a nut and washer. That requires 10 extra minutes and possibly a second person to hold the hardware from below while the person on the roof tightens it. I think your dealer saved a few cents in labor by not using machine screws.
I think I would replace those sheet metal screws with stainless machine screws.
