I got Dirt Rally working last night, and it is working well actually. (other than needing to constantly move your heads to keep the HMD awake. I'm working on that....) If/when I find the solution to this, I will report back.
I seemed to have best success with loading Pimax 1.2.50 (so far)
What needs to be done to get Dirt Rally working correctly is:
-Be sure the HMD is in Pimax mode
Once ReVive is running and shows in the system tray, right click on it, and choose 'Patch'
-navigate to the Drit Rally exe in your \Steam\steamapps\common\DiRT Rally\ install folder to complete the patch.
Files that are required to enable VR will be silently copied to the folder by ReVive.
Once you 'Patch' Dirt rally from ReVive, enable steam VR and when you click on Dirt Rally to run it, it will state that "Dirt Rally does not support VR, it will appear on your desktop, and may affect VR performance", but that is telling you it will be displayed on your desktop as well as the HMD.
(As a quick note. Use the left control key in Dirt Rally to center your view once in the cockpit.)
I hope you can get it working as well. Check out this link about ReVive to see what Software needs to be 'Injected' to, and what needs to be 'Patched'.