Probably for all the myriad of reasons that don't have to do with safety, and in which Nim is arguably better than Rust, C++, Python, or whatever language is most relevant to compare to.
https://andreaferretti.github.io/on-rust-and-nim/
https://arthurtw.github.io/2015/01/12/quick-comparison-nim-v...
I don't think so because the syntax is very different. You would have to learn two languages, and if you know Rust and you need it for safety reasons -- then why not code everything in Rust?
Nim is very practical by design. I think some practical additional security features in Nim (pre- and post conditions for instance) make more sense than interaction with Rust or Haskell. Somewhere I read that the Nim developers plan to add pure functions (like Haskell). This would be the first step in that direction.