C# shares with Java one remarkable characteristic, which is being reproducible. That's the Java motto "write once, run anywhere". It is not entirely true, but for code which:
- does not use floating point types;
- is pure computation (no system calls);
- is mono-threaded;
then tests are effective. This means that you could take the BCrypt.NET implementation, and see whether it is compatible with the reference code. Take care to include tests with non-ASCII password characters, which often are a sore spot. Also, measure performance to make sure that the .NET implementation is not unduly slow (for this kind computational tasks, Java or .NET code can be expected to be about 2 to 4 times slower than C code).
If the .NET implementation is compatible with the reference code, and its performance is not abysmal, then the "reproducible results" aspect of C#/.NET will allow you to conclude that it is ready for production.