I'm from Codeplay and I am not sure about what you mean from your comment about Level0. Intel have developed a back-end for DPC++ that supports Intel processors through OpenCL and SPIR-V. Codeplay has implemented a back-end that supports Nvidia processors by using PTX instructions in the same way that native CUDA code does. PTX is the equivalent to SPIR for Nvidia processors. Maybe I am misunderstanding so apologies if that is the case.
With oneAPI I had hoped to get the inverse, a oneAPI implementation for NVIDIA hardware, but I don't think the CUDA driver API is low-level enough to do so (e.g. explicit vs global contexts). And yes, I know of Codeplay's implementation of DPC++ for NVIDIA GPUs, but that doesn't implement oneAPI Level0 APIs so is not usable for other languages.