Nah, they have a mind of their own. If they like you or if they like your faction, they'll join it, but others will end up joining other factions.
When I defetaed the Kerghit khanate, some of the lords who I beat repeatedly and who hate my guts joined my faction. What sucks is they come into the faction with no lands of their own. Then when you go and besiege a castle, the king decides whom to give it to and since you already have a fief the guy with nothing has a pretty good chance of getting it. So, technically, you're fetching castles to your previous enemies, who still hate your guts even after you've got them A CASTLE and won't let you into the castle even if you're in a hurry, until you become his errand boy and turn his negative relationship into a positive one.
I don't know if there are any tweaks to change their behavior.