We just tag the pipe as well and then use the bottom of pipe hanger elevation in the ITM hanger for our hanger cutlists so they can sticker each hanger with the correct elevation. I'd think you wouldn't want to pull a centerline elevation from the hanger if you could though, because sometimes the hanger size is oversized for the OD of the pipe and the "centerline" of a hanger may not match the centerline of the actual pipe sitting in the hanger.
