Very much doubt if the rears would fit as the ML is a bigger car with different seat mounting points , the fronts maybe physically doable but mounting brackets would need made for the subframe plus there would be a wiring headache to sort out regarding power to electric motors / airbags / heaters etc plus integration into the cars "system".
I recently fitted a set of STi seats into my Forester and it was a complete PITA with mucho trial and error.
FWIW i would try and source a complete W204 leather interior as that would be simpler than fitting seats from a different model.
K