they never seem to activate on my hero or kaiser, but they work fine on my other characters. i'll see if my buccaneer can activate them soon.
edit: just to clarify, aran and evan's character cards give a chance to restore hp and mp respectively every few times you hit monsters. however they do not seem to be working with the hero, kaiser, and also the buccaneer branch. i assume that it has something to do with their self-recovery skills, which restore a small percentage of hp and mp every few seconds, since that is something they all have in common.