you named a bunch of players that were drafted a long time ago. Most euros are scrubs, and only these handful were ever good, the rest are like darko.
I'd guess that Euros who come over as undrafted free agents are more likely to be decent contributors than American players that are drafted in the second round.
They often have a longer track record, so should be better scouted. They are usually more mature players who aren't being brought over as athletic projects who need to learn how to play.
I'm differentiating between Euros who went undrafted and those who were. Teams will often try to bring over a player they drafted because they already invested a pick in him and want to try to get something out of it. Teams are going to have a higher threshold for who they want to bring over if they didn't draft him. Since they often have to make a multi-year commitment to lure a player from a comfortable European setting, they are going to be more careful about who they bring over, less gambling to see if a guy can stick and more recruiting a guy who you see fulfilling a specific role on the roster.