Others have said Rust does not support NonStop.
But, my point is you shouldn't even have to cross-compile Git to a platform like NonStop in order to develop NonStop apps. So the portability of Rust shouldn't even matter here. The app developer should be able to run their Git commands on a supported platform and cross-compile their own app to NonStop.
I haven't double checked, but my recollection of that story was that they were using Git as part of the operations at runtime, not (just) as a development dependency.
Ah, I see Tom the Genius has moved on from using Subversion for his enterprise JSON DSL