After almost 3 months I finally received a very specified answer from Curve:
It is not possible to use Curve Pay on Google Pixel phones, even if the app have been downloaded from the Huawei App Gallery rather than the Google Play Store.
Why it took 3 months and why "it is not possible? That Curve didnt answer and I dont have a patience to wait next 3 months to get some answers, but at least we have a definitive, official reply.
But, things took an unexpected turn - I think the same day I got the answer, there was a GOS update available and Google Pay itself.
And right now, using GOS 20230315 on my Pixel 6a and most recent Google Pay available in Google Play - I was able to add a card to Google Pay and tested it yesterday - it works, I can pay via NFC using GPay on GOS!
Please, check if I'm just weirdly lucky or some things regarding those certification from google etc have actually changed and maybe it also works on your Pixels now?