I was not able to get it added, despite adding my global entry number during OLCI. I called and TAP said it should work, but it still didn't show up upon re-check in. I called again a bit later and they did something, I checked in again (third time), and now it shows "TSA Precheck" in text below the barcode, but not the usual TSA precheck symbol I would expect. Notably, this does not show in the online app boarding pass, but only in the version I had emailed to myself through the TAP website.

So all sorted out, but not through the online systems, and does not show in the app boarding pass, only the email boarding pass.