When you design henchmen, most of the traits that are available also appear during level-up and can be picked a 2nd time - and they function too (not sure about special ability traits like charge though). E.g. if you have acrobat, then choose the path of assassin you can take another acrobat for a total +2 dodge per level bonus. I've also seen champions with 2 strength traits, so I guess they've started with one and then picked it again on the way.
