Blokes like Kaino and Read would go well in League because they are such strong ball runners and attract defenders. I guess it depends on what sort of second-rower the particular NRL club going after a union player would want. If all you want is a tackle machine then union probably isn't the place to look because a tackle count of around 20 is considered high for a forward in union. That's not to say union forwards do less work, it's just that union forwards are less focussed on numbers in the tackle and more emphasis is placed on actually getting to the breakdown and contesting possession.
A lot of bias and misinformation in this thread and as usual the truth lies somewhere in the middle. Anyone with a brain could see that the best athletes in union are freakish and most would go well in league with a bit of training, and vice versa. There are specific skill sets in both sports that would take a bit of learning but as they say, class is class and a bloke like Brad Thorn was able to learn the fundamental skills for a union forward such as scrums and lineouts.
In terms of seeing what union backs are capable of, admittedly international union is probably not the place to start as while the best players are on display, often international matches turn into a grind and the outside backs don't get as many chances. Super Rugby is a better place for spotting outside back talent because it's still the best talent from the 3 best Southern nations but the games are a lot more open and free-flowing. Guys like Ioane and Dagg see a crapload more ball and both look absolutely fantastic at that level.
