One of the roles that Progress (and ATV) fulfill at the ISS is station reboost.
This works because they can dock at the back of the Zvezda module, and boost inline with the station. I cannot find a value for the thrust level of the main engine, but it suffices to boost the station.
A Dragon currently berths to the CBM ports on the bottom (or top as backup) of the Harmony (node 2) module on the US side, and is thus perpendicular to the main line of the station.
But a Dragon V2 will be docking to the PMA on the front end of Harmony (or the PMA which is due to be moved to the top of the Harmony node, and the backup CBM port will be the bottom of Unity, as the MPLM berthed there is due to be moved. See the answer to "Will the ISS need more docking ports" question for more info and images of how the re-arrangement will look).
The front end of Harmony is basically the opposite end from where ATV and Soyuz currently do their reboost tasks.
So will Dragon or Dragon V2 be able provide station reboost if needed?