AMD is working on a cudnn comptability layer iirc (MiOpen) and is ROCm group has created a cuda transpiler (to intermediary HIP then to amd binary via hcc)
Edit: OK I was reading the docs, I think I got it: hipDNN is a wrapper that (once finished) will search and replace calls (from cuDNN to hipDNN), then hipDNN itself, in turn, will call MIOpen, not sure if that's right, I would appreciate if someone who knows more could confirm
Tensorflow uses the cuDNN library, which is closed source. There is nothing for HIP to convert.