When you press Ctrl + R, that's not really a command telling nautilus to reload anything, but rather a keybinding getting caught directly by nautilus. So you can't really bind that directly to a context menu outside nautilus.

It might still be possible to force nautilus to reload by using a dbus command, though. Dbus is a system for interprocess communication used by most gnome software, so it wouldn't be surprising if nautilus too had a dbus remote. I'm afraid a quick google didn't reveal any dbus API for nautilus, but that doesn't necessarily mean that such an interface doesn't exist :)