Absolutely. People who write games or audio / video software sometimes even do hand-written assembly fragments.
The very high-performance things are a relatively narrow area, and an area where C can easily lose to e.g. Fortran.
Also, for ML stuff you likely don't have a huge entrenched C codebase yet. You are freer to choose a more expressive language, and only hand-optimize / rewrite in C a small amount of hot paths.
Regardless of what glue language you use to write ML stuff, if you follow it down to its core, most of it is going to use a BLAS library to do matrix multiplication. That's where the heavy lifting is. And BLAS libraries are in C/C++ or Fortran. For example, OpenBLAS or Intel MKL.
I thought Fortran's aliasing-free rule was just an assumption of the compiler, not something that it actually enforced.. so you could very easily write code that contained aliasing bugs.
The very high-performance things are a relatively narrow area, and an area where C can easily lose to e.g. Fortran.
Also, for ML stuff you likely don't have a huge entrenched C codebase yet. You are freer to choose a more expressive language, and only hand-optimize / rewrite in C a small amount of hot paths.