Given that the Mercedes accessory is tailgate-mounted, I'd say so. Am looking at this myself - I did ask a local Thule dealer and was told that it's not recommended....whether by Thule or Mercedes I don't know!
Fiamma update. The tailgate won’t stay up on the struts fully and sinks - even with no bike on there - sometimes only a little bit and it and stops, sometimes not at all, and occasionally if I hold it up in place then it will stay. I have a telescopic pole I have handy in the back to prop it up.
Similar story here. The trick is to support the tailgate on the way up and then hold it for a couple of seconds - that seems to work. Must admit I don't leave the tailgate up for long