Sure, why not? You can transfer songs and playlists from iTunes just as if the phone is not jail broke. Just do what you've done before - check songs to put on the phone and sync. iTunes will transfer them over and you are good to go.
+1... the only thing you'll need to be careful w/ regarding iTunes is NOT updating when it prompts that a software update is available. Be sure that a Jailbreak of your preference is available (Tethered or Untethered) for that software version first, because updating will un-Jailbreak your device.