Comment out this entire function and try again:
public override bool GetSupportedPlatforms(ref List<UnrealTargetPlatform> OutPlatforms)
{
// It is valid for only server platforms
return UnrealBuildTool.UnrealBuildTool.GetAllServerPlatforms(ref OutPlatforms, false);
}
I just built a dedicated server earlier and had to do that and I was able to get it to build and run successfully.
Let me know if that helps.