So I'm building views in Blend, and using them in my unamanaged C++ game.

In my XAML I can use the older blend interactivity libraries, or I can use the newer microsoft behaviours.
Both work.

I intend to use the newer b:interactivity. But does this choice have any impact on Noesis?

You should use the new b: namespace because it is what our Noesis.GUI.Extensions nuget is exposing to Blend, although internally for Noesis it makes no difference if use one or the other.

Thank you!