Are these graphics card standoffs?

Probably not. No matter how large your card is it should entirely be supported by the screws at the PCIe slot openings at the rear and the PCI slot itself.

There's nothing to screw a standoff to at all to anything in a standard case and these would not be used at all. and it might actually be potentially damaging to the card, placing lateral stresses across the video card or causing it to bow done the wrong way. You may end up cracking a PCB or popping out a heatsink.

As for these additional plated screws, there's no logical consumer facing use for them. In theory you may be able to mount a third party, compatible cooler on it, but your mileage/compatibility may vary, and there's no guarantee those holes are at the right place for it, and it would very likely void your warranty