Grinding a chuck isn't real complicated.
Use a soft wheel so you don't burn the surface. You can also use a small diameter medium hard wheel as the surface speed of the wheel is slower and it will cut softer. You don't need a mirror finish on your chuck, just a flat one with no chatter marks. Dress the wheel course by running the diamond across the wheel quickly, the wheel will cut cooler this way. I then use a wooden stick and run it across the wheel to remove any loose grains of abrasive. Turn on the chuck, in case there is any deflection when it is on. I use a Sharpie and put lines across the entire surface so you can tell when the surface has been completely ground. I also cover the entire surface with cutting wax (available from McMaster-Carr). At the very least use coolant. If your grinder has a coolant system, by all means, use it.
I will start my grind on the left side of the magnet so the grinding is a "climb cut" and then return to the left side along the same path as a "free cut". On my small Boyar-Shultz, I turn the cross feed two full turns and repeat the process. I "climb cut" because it generates less heat. Don't bang into the end stops!
When grinding out a hollow spot or truing up a new installation, take no more than .0004 / .0005 depth of cut to avoid heat build up. If you are getting heat buildup and warping, lift the wheel off of the magnet and reduce that amount. Crank the table at a brisk speed to avoid heat buildup and warpage. Apply a new coat of wax or coolant every time you complete the entire surface of the magnet. Once you clean up the complete surface redress the wheel as before and remark the entire surface. This time use the same technique but only take a .0001 / .0002 depth of cut. Finish by remarking the chuck with the Sharpie and take a free cut over the entire surface. Remember, you don't need a mirror finish, just a flat one with no chatter marks.
One final thought. When stoning dings out of your chuck (or mill table), stone the entire surface so the over time you don't stone a hollow spot into the surface!
Good luck,
Richard