In my very biased opinion.
Ball players
League Players
will tend to be better short passes of the ball, in terms of long passing they both have similar skill sets in terms of long balls, although, league players tend to rifle it out to the winger to give him a choice to stay outside or step back in to score the try because this pass is mostly employed 10 metres out.
Kicking, more flat type kicks into space or mid field bombs or grubbers. Not much going by the way of torpedoes or angled kicks out on the full from the 22 trying to grab the most yardage.
Union players
short passes are ok, but on the whole not as strong, beale and cooper are good at it, its not the passing that is weak, its the sleight of hand and drawing the man that is lax. Long passes are very good, though they tend to be out a fair bit in front, wanting to put the man in the space outside the defender. Though this is changing a bit.
Kicking
as above different types of kicking. due to different requirements in the game.
I was going to do this for each position, but tbh I have work to do.
suffice to say the different games require different skills, league players on the whole will always tend to be better at the tackle, run, pass type stuff.. because that is what the game is.. union players will be better at the possession type stuff because there is more of it then a play the ball.