I have never heard of your service provider, but if it were me, I'd put money on it working. Based on Wikipedia, they use AT&T's network, which works on GrapheneOS.
If you still have doubts, you can safely try GrapheneOS out without needing to worry. One of the things Pixels are good for is they're supposed to be easy for OS devs to mess with, frequently building new OSs and testing them on Pixels. It's very difficult to brick a Pixel. Just follow the instructions on the website and you should be fine.