The question of whether a language is dependently typed only has to do with how type checking is done. The optimizer doesn't come into play until later, so whether it uses the information is unrelated to whether the language is dependently typed.
Rust already does have some level of const generic expressions, but they are indeed only possible to instantiate with values known at compile time, like C++.
The difficulty of type checking them symbolically still applies regardless of how they're instantiated, but OTOH it doesn't look like Rust is really trying to go that direction.