For example, can an experienced coder with limited C#.NET experience be successfully paired with an experienced C#.NET coder with the secondary aim of getting the former up to speed with C#.NET?
Absolutely. Sharing knowledge is one of the points of pair-programming (along with the useful dynamic of having one person type for a bit and the other review as they do it).
In my experience, it's one of the most effective ways of doing so - and allows the less experienced coder still to usefully contribute (it takes less experience to review what an expert is doing and make sensible comments/interventions than to do the entire job).