If I remember correctly, yes, and was "a bit" buggy, so even wine developers discouraged to use it on Linux. But I think it should works a lot better with wine 10.0. I will check it when wine-proton 10.0 arrive.
Well, wine from Valve (wine-proton) has several layers of patches. It contains some patches from wine-staging plus additional fixes made by Valve. And yes, DXVK should work better with wine-proton too. In my opinion, these days it is always better to use wine from Valve (either Linux or FreeBSD) than the base version.