> couldn't an API be exposed from that set of libraries which could be used

And now you've entered that copyright violation territory.

IP infringement, not copyright violation.

A clean room reimplementation of cuda would avoid any copyright claims, but would not necessary avoid patents infringement.

https://en.wikipedia.org/wiki/Clean-room_design:

“Clean-room design is useful as a defense against copyright infringement because it relies on independent creation. However, because independent invention is not a defense against patents, clean-room designs typically cannot be used to circumvent patent restrictions.”

> A clean room reimplementation of cuda would avoid any copyright claims,

Assuming APIs are either not copyirghtable or that API reimplementation is always fair use of the API, neither of which there is sufficient precedent to justify as a conclusion; Oracle v. Google ended with “well, it would be fair use in the exact factual circumstances in this case so we don't have to reach the thornier general questions”.

I didn't read the GP post as talking about clean-room reimplementation, but rather just serving the same NVIDIA-written libraries on top of AMD hardware.