It's VERY similar! I took the ACS last June and took the DAT in the beginning of October (got a 22 in o chem), so its format and question types were still somewhat fresh in my mind. I studied my ACS study guide book for the DAT o chem. DAT Destroyer is, of course, the best prep for DAT o chem questions, but the short section tutorials before each section's questions in the ACS book are the review you need - only condensed. I thought it was great. Plus, if you've taken the ACS exam, you're already used to taking a multiple choice o chem exam, which is a far cry from most o chem midterms through out your undergraduate classes.
So ya, ACS book = even more review for the DAT in terms of more practice questions, but more importantly, condensed info on EVERYTHING (that's important) you learned in your o chem classes. Use it to SUPPLEMENT DAT Destroyer, it will help you immensely when you don't want to sift through 700 pages of your o chem text book.
I agree, I recently scored a 30 on OC and I too took the ACS exam and scored quite well on it. I started out studying for the Organic Chemistry by reviewing Kaplan's notes and then approached DAT Destroyer. I also bought into Chad's videos and by far the combination of Chad's videos and DAT Destroyer are what solidified my performance.
I then used the ACS prep book to review some of the various types of problems and noticed that once you had a really great understanding, you can blow through all the review/questions in a day. Once your at that point, you are definitely ready!