There's the amdpro drivers, which nobody uses; they're partially open source, as I understand it.
The point is that AMD releases detailed documentation for every GPU they sell, and thus it's very easy for mesa to support their hardware; AMD themselves also contribute code to Mesa, of course. This is in contrast to NVIDIA, which even uses encryption and signatures to twart nouveau efforts. I avoid NVIDIA entirely, for this reason.
I haven't had issues so far. Life has been good, same as with the vega 64 on my workstation.
Have you had any issues you suspect may be driver / gfx related?