There is no grommet per-se, but there should be an oversize hole below the headlamp assembly to lead the tip of the headlamp assembly "skewer" into an all-metal spring clip that forces the tip-end of the skewer to an exact position within the hole. I never looked to see how that hole and spring clip is attached to the vehicle structure or if it is an inherent part of the structure, but I suspect if you investigate, you will find it to be there - I could be wrong.
So - with the headlamp assembly removed, if you fully insert the skewer thru the hole in the upper radiator support while keeping the skewer perfectly vertical during the last inch or two of insertion, does its tip not automatically lead into the hole I mentioned, with a metal finger pushing radially against the tip of the skewer, causing friction while it pushes the tip to a definite position within the diameter of the hole?
A little extra information on installing the skewers with the headlamp assembly installed: There are machine threads just below the heads of the skewers that engage the plastic hole of the headlamp assemblies. It is important to be gentle when installing and removing the skewers not to over-tighten when installing, and not to press down too hard with the screwdriver when removing because the soft plastic threads in the headlamp wear and are easy to strip out from over-torqueing or pressing downward too hard with the screwdriver. Some downward pressure is necessary to keep the screwdriver tip from slipping. Early-year skewers actually had torx heads (no downward force required); later years had Phillips heads (downward force required). (My '98 Concorde had torx heads; my '99 Concorde had Phillips heads.) If you're ever in a salvage yard and come across a set of skewers with torx heads, you might want to grab them.
When tightening the skewers, you'll notice they lift the headlight assembly up to clamp them against the upper radiator support. Tighten the skewers just until they start clamping the headlamp assembly against the upper radiator support, and then stop tightening once they are only very slightly snug to prevent unnecessary stress on the plastic threads. If the plastic threads do strip, from then on, to remove the skewer, you'll need to put upward pressure on it using a flat-blade screwdriver tip under the head while turning the skewer with the Phillips driver. And it may be difficult to keep the headlights pulled up to the upper radiator support when installed.