https://publicintelligence.net/u-s-navy-f-18-natops-flight-manuals/
US Navy F-18s use the AN/ARA-63 ICLS receiver, which isn't compatible with "proper" ILS. While the ICLS, technically speaking, is an instrument landing system (and is referred to as such in the natops flight manual), it has nothing in common with standard ILS. It has more in common with the TILS system used in the Viggen (pulse coded sweeping azimuth/elevation beams).
Land-based export models of the F-18 may be equipped with different avionics for use with civilian navaids.