DFC
I wanted to clarrify Charley's interpretation which I guess you have done.
The position would seem to be you are not required to have an FM immune VOR outside controlled airspace to operate IFR.
My understanding is that the VOR has to be placarded "not FM immune". I know of many aircraft with this wording so I assume the avionics chaps know what they are doing. The placard does not say the equipment is unserviceable. In exactly the same way the comms boxes may not be FM immune, but in that case there is a specific exemption permitting their use in controlled airspace. In my opinion your comments are therefore misleading becasue you are legally entitled to use the VOR other wise the legislation would be worded in the way it is for the G/S. An all together different debate is whether you should rely on a non FM immune VOR as the sole means of navigation. I guess their are many aircraft with the G/S FM immune but not the second nav box for example. Equally there are those perhaps with neither FM immune but with a GPS. Perhaps again there are those that understand how to fly a DME arc.