Re: Going from C# to C++...
In a previous job I saw candidates come in who had C# experience primarily and they did well. They were bright and I think they had had some knowledge of C++ so that helped.
I didn't go that direction myself as a C++ programmer so just something I observed really if that helps.
I'm sure there be other responders here who have done the transition for themselves.
On a side note, you can always figure out their ability to pick up C++ by getting them to complete some coding exercises in the interview if they look like strong candidates.