I came from a Pro-C to a G2 Rachio.
Yes, your two white commons should be able to go to either Rachio C terminal.
The Ground terminal from your Hunter should be part of your power cable for the Hunter Pro-C and not used with Rachio as its power cable assembly hands ground.
The P/MV is I believe your pump/master valve terminal and would go to the M terminal on the Rachio. Don’t forget to enable it in the Rachio app settings. I don’t have a master valve so I can’t say for sure.