Unlike the other adaptations and remakes -- the movies, the comic books, the Paperback Library gothic romances, the 1991 revival series, etc. -- which are different versions of Dark Shadows from the original series, and which could be thought of as taking place in separate, parallel universes, the Big Finish audio dramas are supposed to be consistent with the original series, set in the same fictional universe, or continuity, as the original series, so that, for example, the Jamison Collins in Big Finish's "A Collinwood Christmas" is supposed to be the same Jamison Collins who appeared in the original series.
In other news: Are you certain the Collinsport rooster sound effect was never used in any of the pre-Barnabas episodes?
No I am not 100% certain it wasn't used in any of the pre-Barnabas episodes. I have been looking out for it though. Between that and Grayson Hall's golden facial gestures and even Dennis Patrick's "finger gesturing", I find a certain degree of comic relief. :)
So no, I'm not certain of it. If it is heard, i'll make sure to edit it in.