halflings break the princess rule about as much as knights do, if you decide to make them all noble and courageous and simple, then sure its princessy, but theyre no different than a knight in shining armour that way. plenty of evil or questionable halfings in dnd, theyre no different than dwarves or elves in that regard.
as for the need for them, i dont see any specific need. if i were to think of where they ought to go, id put halflings in with the kuriotates, would be a good replacement for their archers (slingers) and the kuriotates are a mixture of races (and frankly theres not enough races represented yet), plus cardith is practically a halfling already heh