Rust is statically typed and doesn't have null returns, so it's got advantages for correctness, but the big win with Rust vs. Python would be performance, not security.
There's a lot more checks and balances built into rust as a language, so the foot-gun opportunities are less likely - which makes it rather suitable for reliable systems programming.
And getting back to this particular case... kanidm is fast AND reliable. There's a lot of testing going on comparing it to 389 DS.
Yes, I write a fair bit of Rust. I'm just saying: between Python and Rust, there isn't that much of a security difference (you could nitpick things like deserialization in Python, but really the significant security win of Rust is not having memory corruption flaws, which Python has never really had.)
