Yes , I use the the Bilstein rears on my +8. IIRC they are the units which were specified for the Series 1 Roadster, which was set up as "soft" as MMC dared to use at that time.
It does make the rear end slightly more compliant over the gentler bumps, and due to the the fitment of bump stops inside the units , it does seem to cope with the larger hits as well.