The FARs require a check of the VOR receiver before IFR flight:
§91.171 VOR equipment check for IFR operations.
(a) No person may operate a civil aircraft under IFR using the VOR system of radio navigation unless the VOR equipment of that aircraft
...has been checked using a procedure described immediately following.
Does this apply to an ILS approach? Specifically, consider a flight conducted entirely using GPS, except that it terminates in an ILS approach. In most (or all?) aircraft, the ILS and VOR receivers are one and the same. However, the mechanism of how an ILS and VOR work are very different.
The FARs speak of "the VOR system of radio naviation". Is that specifically for actual VORs, or does it encompass the ILS by virtue of being the same receiver and CDI?