I recently used the mobile passport control/customs app (coming back to the US from Montreal). It was a huge help through customs. The line was literally hundreds of people long, and I breezed through in less than 5 minutes. My plane was delayed by about 40 minutes because of the line, and someone who boarded said those who used the app went through the line faster. I also have global entry, so I thought that's why I skipped the line.
With that said, it did not ask me any questions about contact tracing or anything like that. They were just the standard customs questions that used to be on the paper form. The email I got encouraging me to use the app also did not say anything about contact tracing.
My emails about check in also did not say anything about contact tracing. I have flown internationally several times in the last year and have not seen anything like that, but none of those flights were on AA.
My suggestion is to ignore the email (to the extent that you can), and check in and download the app and proceed.