Please notice that any function called from C# isn't safe because a cracker can change the result in your .NET application without modification of the protected DLL.
Doesn't matter if they modify the C# application since it only processes and displays data through the protected DLL. They would need to modify the DLL for them to do some damage.
My question is if Exported functions that are protected are as safe as normal ones.
Edit: also doesn't matter if they change the real data in c# app since it would be useless and just a fake screen since most requests are processed by a server.