Scott, Yes & No.
You can use pitch correction software such as Antares but not Vocal Harmonizers such as DecaBuddy or VoiceMachine. These require an Audio Input Bus where you can install an effect such as DecaBuddy. Also DecaBuddy needs to see the midi notes you are using for creating the harmony. It is sad that Cakewalk have not seen fit to add this option to both Project5 and Sonar 4. Cubase has this feature and so has forte Ensemble.
[This message has been edited by Frank L. Rosenthal (edited 06-20-2005).]