The API is identical so you shouldn't have problems reusing the diagram related code in your WPF application. If you save your diagrams with the built-in serialization methods, use the XML file format to be able to load them in our controls for other platforms.

There are some node types that are available only in the Windows Forms version - such as SvgNode and CompositeNode. If you are using them, better create a derived node type that you can implement later in WPF using similar features; e.g. you could replace an SvgNode base with ShapeNode and display XAML drawing instead of SVG drawing, or replace a WinForms CompositeNode base and its XML template with a WPF TemplatedNode and XAML template. This will localize the required changes to just the derived classes, so you won't have to replace node types all over your code.

I hope that helps,
Stoyan