We use Codesmith to generate some code, and when we open up the projects, the files are there, in the solution, but there is no way to check them in. The DLL compiles just fine. The only difference to the .csproj is the addition of any new files we generated.
But unlike VSS, TFS, does not detect these files. I validated this behavior by editing the .csproj manually. For some reason, the only way to add a file to TFS is through Visual Studio.
However, when I remove them from the project, and then include them, I get the usual yellow plus sign.