Surely any aircraft in IMC is receiving a minimum of RAS? And so the question is not relevant - you have to rely on ATC for separation? Please don't tell me people fly in IMC without such a service A RIS would for me, be risky, but anyway, the service provider should be giving the traffic information.
Nigel, in the event that you discover there is no radar service available for part of your route in Class G, what would you do, turn back?
Unfortunately, we do not have the panacea of a full LARS coverage in UK, if anything it has reduced in recent years. Some of us certainly do have to "make our own arrangements" at times whilst flying in IMC in Class G. That is why I, for one, could never opt for FLARM instead of TCAS. I don't have the choice of cancelling a flight because of IMC conditions en route, at least, not if I wish to keep my job and not give it to someone else who would willingly take my place.