It's one of those debates that can really work either way. I think it's really a matter of how well you want to filter/clean your tank water and what method you prefer. The refugium idea is to create a natural filter for cleaning the water using macro algae to obsorb excess nutrients and having pods and other creatures to eat the detrius and other material. It also acts as a safe nursery for pods and such animals that will help replace the ones that naturally dissappear in the main tank. The placement of the UV sterilizer and even other equipment has pros/cons no matter wher you put them. If you put it before the fuge, then it will kill off some of the stuff that the refugium needs thrive. But if you put it after the fuge, it will kill off some of the good critters that travel from it to the main tank. Of course this is if you have the entire system setup to filter in line.

I would think it best to have the UV on a separate loop that either dumps back into the tank or into the return area of a sump instead of dumping into the refugium and having the refugium fed by water straight from the tank. But then some would argue that the UV is not really filtering 100% of the water in the system. Of course if your system is filtering the total water volume a few times an hour as it should, then all water will eventually pass through the UV.