Thanks TwinsPoppa and rogerkiu for the replies. I am with you on the error coming down to either the sensor or the DSC unit with my first choice being the sensor.
With that in mind I did order new sensor from ESC (noted that have bosch unit for $349 vs BMW at $512)
BMW E53 X5 N62 4.8L Search SiteSearch 34526777435
Given the info posted by TwinsPoppa in his thread last year I was almost opted to try the older part number with a used part via e-bay but did not.
Just as luck would have it this morning our son managed to nicely place the Toyota van in the snowbank between driveway and yard.
So at 6:15am in -12F degrees I found myself hooking up my tow strap to X5 hitch and getting ready to curse the lack of 4wd as the light has been on steady last 2 weeks. Turned the key to start up and the light went out (no joke), using the two strap and recovery bar in the X5 hitch worked easy and pulled the van 15 feet back onto the driveway right up the hill.
I did have a pretty good laugh later when I checked mail to find that ECS sent confirmation of my order being shipped for the speed sensor.
Few trips today over 3 hrs and the 4x4/DSC light has stayed out entire time. This evening I hooked up GT1 again to confirm my earlier question.
YES the angle sensor does report data LIVE in GT1 when it is working correctly Control Units -- DSC-->Sensors-->select them all. Gentle shaking or rocking of the X while parked with key ON (motor off) shows values updating quickly for both Rotational rate and Transversal acceleration. Few days ago when the 4x4 / DSC light was ON (GT1 found DSC - 5F0C DSC : DSC sensor, internal –Fault currently present) both of these numbers were measuring fixed at 0.
New sensor is due in a few days and I will still replace since this condition has been intermittent. The failure here looks to be same as what TwinsPoppa encountered but only with 4x4/DSC light on, I have had no other lights , no suspension inactive/faults.