NVidia will actually ships the denoiser as part of the OptiX 5.0 SDK so anyone can integrate it in their application. I've looked at the OptiX samples briefly and it doesn't seem too complicated to use it. The denoiser can be used separately - the renderer itself doesn't need to be done with OptiX or use GPUs at all.
However keep in mind that the OptiX denoiser *requires* an NVidia GPU in order to run. If you wanted to use it on a render farm for final frames, you'll need GPUs on the farm (which is what NVidia wants, for sure :))
Best regards,
Vlado