C++ Library for implementing a web services api over legacy code?

To fix this issue Both are really good options. It really depends on your expertise in your team. If all you know is RPG, use the RPG solution. If you have someone with .NET or Java experience, then use that.
If you have more questions related to this, there is a great community of developers that can help on the Web400 mailing list.

Hope this helps WCF comes with a set of standard bindings, here is a list of the bindings provided in 3.5:
http://msdn.microsoft.com/en-us/library/ms730879.aspx

it fixes the issue You were probably almost there with (2). Be sure to turn off contract re-writing for the C# assembly you construct by hand. Turn off all run-time checking and static analysis and the re-writer shouldn't kick in. Put it wherever all your other CodeContracts assemblies are going, e.g. for /bin/X.dll, make an assembly that goes to /bin/CodeContracts/X.Contracts.dll.
See http://social.msdn.microsoft.com/Forums/en-US/codecontracts/thread/5fe7ad4e-d4f1-4bb5-806e-a1e31f550181. You were right -- just create all the right bits by looking at Reflector and it works out. I wanted to do this to add contracts to my F# assembly until F# can handle contracts.

Any of those help The key item here is to pick the point that you are actually going to unit test. In your case, putting a test on the exact method you are replacing doesn't make sense. Instead a test needs to be created for every point in the application that calls your method to ensure that the specific functionality still works the same.
The reason is that once you have completed refactoring the DataCreator class you will have to go back to all of the areas that call it and change those. Putting tests on those areas prior to making changes will ensure that your functionality is the same.

public class SomeClass {
  public Boolean DoSomething() {
    OtherClass oc = new OtherClass();
    return oc.DoSomethingElse("param1", "param2") == "true";
  }
}


public class OtherClass {
  public String DoSomethingElse(String param1, String param2) {
      // horrible code here which never uses the second parameter

     return "true";
  }
}

seems to work fine I'd say this logic belongs either in your MockOrders.Order class, in a class from a higher layer which uses your Order class (e.g. BusinessLogic.Order) or in a Label class. Sounds like your label acts as a joining attribute so, without knowing the particulars, I'd say pull it out and make it an entity of its own, this will give you navigation properties so you can more naturally access all Orders with the same label.
If modifying the DB to normalise out Labels is not a goer, build a view and bring that into your entity model for this purpose.