I had a similar question about this particular recipe and it does seem to be a bit confusing. As noted it is the only rum suggested in the list of rums on page 198 (I think the full list covers pagess 197-199 but I don't have the book in front of me at the moment). I was making the Dr. Funk on Friday (without the seltzer which I found unnecessary and in fact detracted from the drink for me). The Hamilton Jamaican Black Pot Still Rum indeed appears to be a unaged or young rum colored with "double strength black caramel" and I suppose what makes it more distinctive from the Hamilton Gold is the percentage of light versus heavy pot still rums used in each blend for these bottlings. The coloring alone can't be the only difference can it?
Interestingly the pdf implies that both Myers and Coruba used to fit this category but in the opinion of Ed Hamilton (I presume) no longer had the traditional character found in earlier versions of these rums. Will have to check the list in the book to see if Myers (unlikely) or Coruba are on the list at all. Coruba was my go to for Hurricanes when I can find it but if the Hamilton will do it would be nice to have an alternative.