Traveling to ORD in UC with hand luggage only and was wondering whether I can simply use OLCI and make my way straight to the private security channel lift and scan in my printed boarding pass. Under the new ESTA regime is there any requirement to actually see a check in agent to have my boarding card endorsed or ESTA status checked ?
You don't need to see anyone. Passports and boarding cards are not stamped as 'ESTA Checked' or anyting like that.
ESTA is designed to be an electronic system so why add unnecessary manual steps?
As long as the passport you are using on this trip is the same as the one you used when you applied for your ESTA then you will be fine (assuming your ESTA was approved of course!). If you have a new passport issued then you need to reapply for ESTA as its linked to your passport number.