No, Play Integrity intentionally checks if it's a Google-approved key. Android itself has an API to check verified boot and gives info on the signing key - most devs just want to know verified boot is working.

I feel Play Integrity has a short life ahead of if competition authorities realise how exactly it works. "Anti-competitive" is the first thing policy-minded folks think when I explain the API to them.

I would guess that it allows to detect tampering if you have to give your phone to the security officers and they do or don't do something with it without you present. I heard of such occurrences on the border, but this happens in other places and countries, too. Not sure if locked bootloader would help, though