You could use epoxy - no prob. Our BondTite 1101 as a primer adheres to most metals, so you could even epoxy the grate to match the floor.
Your's is a new floor - but here's how another board member handled a [URL="http://www.garagejournal.com/forum/showthread.php?t=23397&]existing drain problem[/URL]
If you're going to be epoxy coating soon a quick way to fill cracks, holes or other voids is to whip up some epoxy patch. With our BondTite 1101 you just need to combine 1 part of the mixed BondTite with 6 parts of fine, clean, dry sand - often labeled "playground sand". Now that makes a pretty thick epoxy based mortar, but it's self priming and will adhere real well to the prepped concrete substrate.
With some work you can get quite a smooth finish, but that does take a bit of practice, expect a rougher finish first time out. Of course a thicker application of epoxy, or extra layers, is a quick and easy way smooth the finish if needed. And as always a broadcast of flakes covers a host of sins.
You can overcoat it with a primer coat of more BondTite 1101 as soon as you're able to roll or brush over the fill without pushing it out or leaving marks, depending on size and climate that can be as little as a few minutes.
This can also be used when you have a depression to fill, with spalled concrete, or to fix up an earlier patch that's failed.
