In DayZ, go to options > video > and set your resolution to 1280 x 800 and full screen.
Also adjust any graphics settings you may want to change for running in the rift such as lowering details, shadows etc.
After saving graphic options go to options > controls > controller and select OpenTrack and click enable, the save settings, and close the game. (I found the the head bob was a bit much when in the Rift so I turned that way down, and you may want to also before closing out.)
Navigate to My Documents > ArmA 2 and find the file called yourusername.ArmA2Profile and open this in a txt editor. Scroll all the way to the bottom and you’ll find two options for fovtop and fovleft. Change to the following to get an FOV of 90.fovTop=1.0297443;