It depends if the bar is factory fitted. If so, it's a TJM bar and Nissan didn't provide an alloy winch bar option from factory.
A winch cradle will allow you to fit a winch, you'll also need to have a metal support that slots in the back of the alloy bullbar for the fairlead to bolt onto (the alloy is then "sandwiched" between the support and the fairlead) because the alloy bar is not designed for the lateral loads generated by people who insist on winching at a 90 degree angle to the direction of the vehicle.
Unless you're keen on a competition winch bar (Cheezy racing, etc), or a custom/DIY jobbie, I'd buy a steel winch bar from ARB before they stop selling them. Quick! Go now!
Food for thought: Toyota's present day factory fitted combination of an alloy bullbar, winch cradle and fairlead support weighs more than the steel winch bar.