Kelsier was hero to me atleast. I believe his passion for killing nobles stems from what has happened to him, nobles kill, rape and treat Skaa like they arn't even people. Many of Kelsier's friends (such as Doxson) have personal loss due to the Nobility. Another thing is the fact that Kelsier knows the Nobility have some power to change how things are, but won't. To him, this is them upholding the Final Empire. Sure you could argue that killing nobility with enjoyment is villainous. But in the context of the world and story, he is only doing it because of all the casual deaths of Skaa the nobility cause. He definitely isn't evil, just has alot of inner demons, mostly because of what happened to Mare.
At the end of first Mistborn novel, Vin shows Kelsier that not all nobility are evil and so he stops the order to kill them all. I don't even think he is psychopathic, I think he just wanted to end the Empire that slaughtered millions casually, and killed the woman he loved. In the end he just wanted freedom for the people.
Also no, I don't think that would even be the case if they met. They both are upholding justice and fighting evil in their own times. It is also mentioned at the end of the Alloy of Law, when Marsh meets Marasi that Wax is "doing my brothers work, and that is something I feel inclined to encourage."
But hey, that's just my take on it!