I'll actually answer your question. I asked the original question about Special vs Regular, but I did not brew this recipe. However, I have enough experience now to give you at least some insight.
The OP stated "Black IPAs should have enough dark malt flavor to justify their color (not using only Carafa III)", which, IMO, implies that he/she thinks that using only Carafa III would give you not much roasty flavor, and would only really contribute color. This is the opposite from true, so the OP is confused somewhere along the line. So its unclear whether the OP knows the difference between Special and Regular, and its also unclear whether the OP meant they did not have experience with specifically Dingeman's Debittered Black malt or dehusked black malt in general.
For my approach to a Black IPA I used a larger quantity of dehusked black malt for my color and roast flavors ... almost 10% (it was session strength so number might be misleading) and I liked it as a starting point, maybe a touch on the roasty side.
As far as this recipe, I would guess at 3% chocolate malt and 3% dehusked black malt you would be in the right range. The chocolate malt should get you there in terms of having enough roastiness. That much husked black malt with the chocolate malt would probably make you in more of a hoppy porter range.
Cheers!