Once again for those who don't understand:
The only reason why Nvidia can get away with a binary-only blob is that they don't use any part of the kernel, they reimplemented everything in their blob. They only interface with the kernel.
DMA_BUF integration would mean that they are sharing certain GPL-ed parts of the Linux kernel with in-kernel drivers. You cannot shim around this because you must use the same code that the Intel driver uses. Whatever part touches this is derivative of the Linux kernel.
Nvidia's licence prevents this. That's the end of the story. You cannot just rename a symbol and then claim that it's legal.