Both. See https://github.com/uncomplicate/bayadera too.

Whatever the language, you have to make function calls to cuDNN, because cuDNN is optimized by Nvidia, which put serious resources into it. Even if you wrote everything in C++/CUDA, you probably can't match it for the standard stuff.

The custom things that I write, I prefer to write in CUDA kernels + Clojure management code.

Clojure kernels are technically possible in the same way as Julia or whatever kernels are possible, but the thing is that you have to match low-level hardware features anyway, so CUDA C/C++ just makes more sense for kernels, which are tiny part of code anyway.