The BAR-97 Emissions Inspection System (EIS) should recognize your 2007 MBZ S600 as a CAN equipped vehicle and should (if the vehicle information is entered properly) omit the OBD-II portion of the smog inspection automatically. If for some reason the Vehicle Lookup Table (VLT) in Sacramento has a glitch and the smog machine prompts the technician for OBD-II testing, the smog tech should bypass this test by instructing the smog machine that your S600 is equipped with a CAN system and not required to undergo the OBD-II test.
As far a the "stable RPM" issue, a smog station with the latest in RPM ignition pickup equipment should be able to pickup the RPM signal. Mercedes Benz vehicles are notorious for having problems with ignition signal pickup due to heavily insulated ignition wiring and components. This provides a benefit when dealing with crossing CAN signals but does pose an issue when using a non-contact RPM signal pickup device.
