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.