This question sounds vaguely familiar ...
I know for a fact that Commontime's mNotes requires the standard Domino Directory or Personal Address Book templates (which, for contacts, are essentially identical) to sync with.
So, mNotes would NOT allow you to sync to a PDA from a dircat.
I can't state that as emphatically for other sync products, but my bet would be it's the same answer.
However, as the other respondent said, mNotes allows you to sync up to four address books - you could just go natively back to the original books you condensed for your dircat.