We need to better know how much of the area swept by the VAWT would be taken up by the Sharp rotor. It would be like for a Darrieus turbine with a Savonius rotor inside to help starting.
What interests me about Sharp or Flettner rotors is the possibility of coupling them to VAWT so that they form a rotating unit, with no moving parts relative to each other. If, in addition, the blades are light, for example by using shapewave® technology, this could be a possibility. But all this remains hypothetical.