Royal Ambassador and other status in hotel groups is definitely stackable with Virtuoso (and I think FHR ) bookings - all you need to do is to have your agent have your membership number added to the booking.
Also Virtuoso rates at least can be cheaper then 'best flexible' offered on hotels websites - on a booking at the Mount Nelson some time ago the rate was considerably under the rate offered by the hotel and my recent stay at the IC Hotel Dieu in Marseille the rate was only slightly higher than the discounted rate offered to members but when you add in the amenities it was a much better deal.