Yes, a standard #6 screw of about 3/8" thread length (need to verify this as you don't want ones that are too long) with a washer could work, but a proper screw for mounting HDDs with grommets should be shouldered so the screw cannot be overtightened (potentially eliminating the damping effect of the grommets). From the picture at the Antec link I posted, they don't look as it they are shouldered (at least in the way that I mean), but they do seem to have fixed washers. So generic would probably be fine in this case plus you could buy the screws and washers in stainless steel (Home Depot/Lowes or your favorite, well stocked, local hardware store) and still come out way ahead of the Antec price.
.bh.