In such scenarios, the assembly routines lend themselves to relatively easier manual scrutiny - given that they are smaller in size compared to the much larger higher level language code in the project.

It's the latter that really needs the compiler's assistance to help remove memory safety issues (it is much harder for humans given the code size and complexity order). The fact that that safe higher level language code is inter operating with inherently unsafe code (as per the Rust definitions) is absolutely OK.