I agree with Chris on that point - I also think the SOP should say "American Dominique". But that's a matter of personal preference and something that has been debated among breeders forever back and probably forever forward since the breed was known. Really, anytime we write it as Dominique (not just dominique - note capitalization) we are referring to the breed, but that's splitting hairs. Anyway..
As far as the Dominique or American Dominique being used in the breeding of the barred Plymouth Rocks, I believe the history lesson the standard is giving us is that it was not a rose combed fowl but a single combed one used. Okay, fine. But at the time the BPR was being created there was little to no distinction between the rose comb, single comb, dominique Leghorn, dominique Game Fowl and the bird we know as the American Dominique. What someone would call a Dominique in one county would be called a barred Leghorn in another - unless those folks happened to be well versed enough to realize the difference in ear lobe and egg color. Many of these birds probably got crossed together, then culled out by the best breeders, to finally find what we know today as the American Dominique. To say they were only comprised of Java, Hamburg... stock is impossible to honestly state. If you saw a cuckoo, rose comb, yellow-legged, red-lobed rooster today with incredible Dominique type and color, would you not call it a Dominique, even if you did not know what stock it came from? I am NOT saying that such a bird would be put in the breeding pen with out some testing, but what I am saying is that our poultry breeding forefathers were selecting for the best traits - not the specific comb, long before the APA was around. That is why the Dominique that is familiar to us - the upright, medium size dual purpose bird (with rose or single comb) was so popular long before the standard was written.
So, after a much longer than I intended post, I don't know that any of us know for sure that it was not simply a single combed Dominique used for the BPR.
And many of the best Dominique breeders to ever live have kept and bred single combed birds. No, you cannot show them, and if you have more than say 5/100 chicks with SC you need to correct it, but many of the great breeders would keep SC hens noticing more vigor in their male offspring. Only recently have we learned there is scientific fact to this - the rose/walnut genes reduce sperm (mobility?) so a Rr male will have better fertility than his RR counterpart, all else being equal.