SFML2 doesn't use any NSViewController/NSWindowController. However, you can get the underlying NSView/NSWindow with sf::Window::getSystemHandle().
sf::[Render]Window sfwin(...);
NSWindow* nswin = sfwin.getSystemHandle(); // will return a NSWindow*
If you create your SFML area inside a NSView/NSWindow (see Cocoa example) you can also get its underlying NSView/NSWindow.
sf::[Render]Window sfwin(nshandle);
NS[View|Window]* nshandle = sfwin.getSystemHandle();