I don't think Dragon has 200m/s when it also has to push the entire ISS. Dragon's "Boost Trunk" provided a whopping ~1.5m/s to the ISS late last year, and that thing is about as big as the Dragon capsule itself.

Pretty sure the ISS doesn't have the radiation shielding you'd really want for that trip. It'd be limited on acceleration in order to not break apart, so it'd be a long trip in open space.