Thank you for your queries. I think Octane team already mentioned couple of important points in their reply:
- most of the Octane code in CUDA, hence it has a dependency on CUDA devices.
- they are porting Octane over to a new framework that cross compiles to Metal/Vulkan/CUDA to support other GPUs
As this is a third-party software, I guess they can provide you more information regarding your queries.
By the way, we have a separate ProRender community, you may like to check it as well.
Thanks.