Meaning Rust is being used in the Android OS itself, so this isn't about app developers?
For Android you write JNI bindings with something like rust-jni.
So yes, you have to write bindings twice. For an example project check out https://github.com/dbrgn/candidateparser and https://www.reddit.com/r/rust/comments/7aam04/meetup_slides_...
But it's not something ordinary Android developers need to pay attention to.