is it possible to mimic hardware decoding by passing the stream through an intermediate software layer that uses OpenCL or CUDA for the hardware assist?
Your link is just to a software layer that takes advantage of any hardware present on the system i.e. on an intel system with vp8 hardware decode it'll use that, if not then it'll use software.
edit: on a second read I see your link intends to create a GPU accelerated VP8 decoder backend for those libraries, not just create the interface layer.