Grey cards are just a form of communication with the colorist, giving them a neutral color & exposure reference in case the scene that follows is deliberately not neutral or exposed differently than normal.
But if you are going to be there with the colorist then you can communicate with them directly though it still is nice to have a grey card to set-up with as a starting point, assuming you shoot it correctly.
But in terms of getting a scan done to log DPX files, that's done to standards to capture all of the information on the film, it's not balanced to a grey card anyway. But if you are then getting Rec.709 gamma dailies of those log scans for editing, then a colorist would do a pass and if you weren't supervising, then a gray card is a good reference for them.
For example, let's say your scene was deliberately dark and golden -- a colorist might make it neutral in color and brightness, not knowing whether the underexposure and color cast was deliberate.
Or maybe you're rating 500T stock at 320 ASA -- the colorist may or may not correct that overexposed image (denser negative) back to normal brightness.