NDepend is more about code structure, code quality, code metrics, code diff ... It doesn't know about string constants content, so this is not the right tool for what you need to do.
For that I'd advise using Mono.Cecil which is an assembly content reader API (OSS/free) pretty well done! Btw NDepend relies on Cecil for reading assemblies and I can say it is a great API with high performances and pretty close to bug free!.